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Is it possible in cg miner or guiminer to only mine with four of the five Gpus I will have connected?

Yes.

As for the builds you can make it cheaper by running some live usb linux flavor (e.g. Debian) as the OS, so no need for the drive and win7.

You can also save by using a dual core and a cheaper mobo (different socket), if you're gaming for only 4h a month do you really need a good cpu?

No need to buy a case too, more money saved.

Hi, guys. I have about £2500 to invest in litecoin rigs. One of the rigs is a replacement for my Sandy bridge rig and will be a gamer/miner, I will use it to game maybe 4 hours per month. The other rig is a cheap AMD platform. The haswell rig will run with my 7970, a 7950, and a 6950 I will purchase. The AMD build will run 4 7950s and a 6670 or super-budget card for displaying the screen w/o compromising the stability of the cards that are mining. Is it possible in cg miner or guiminer to only mine with four of the five Gpus I will have connected?
 
Here are the two builds, can they be improved?

Gamer/miner
I5-2500K
Gigabyte GA-Z68X-UD5
XFX 7970 (owned)
Sapphire vapor-x 7950
HIS or Sapphire 6950
Corsair HX1050 (owned)
Lian li T60
Optical drive, win7 h

Edit : updated build

The 7970 gives around 600kh/s, the 7950 should give around 600 too and the 6950 will get 400-450
Total hash rate : ~1600kh/s

AMD
Athlon ii x2 270
Gigabyte 990FXA-UD3
4gb ram
4x sapphire vapor-x 7950
6670 (to power display)
OCZ 1250W psu (might get a 1475w to be safe)
Optical drive, win7 hp
7950s will give around 600 each so 2500kh/s should be achievable. 6670 will give around 50kh/s should I decide to mine with it too.
Total hash rate : ~2500kh/s

Combined hash rate: ~ 4100kh/s

Thanks for your time!

You may want to rethink the Gigabyte 990FXA-UD3. I have one and it is difficult to mine with unless you are planning on using extenders, also the passive cooling on the board leaves virtually no space between the heat-sink on the board and one of the GPUs.

Why is it difficult to mine with? Also what am3/ am3+ board would you recommend for use with risers?

I'm glad someone mentioned mobo issue.  I hate that mobo.  I have about 10mh, about to be expanded to 15mh in a few weeks once I settle into my new home.  You can't go wrong with MSI Z77G60.  Except you'll have to change your processor to an Intel 1650, preferably an Ivy Bridge proc if you want that last PCIx16 to be active.

I don't have too much experience with other GPUs, as the Gigabytes have worked well for us (if it aint broke don't fix it), but I think I've seen vapour-Xs in other people's builds.

Don't crossfire the cards. This can lead to problems and lower hashrates in Windoze and is not needed for mining. Crossfire doesn't seem to have an adverse effect on my linux box for some reason, but it isn't needed so there's no need to take the risk. If you want to use your rig for gaming as well as mining then just hook up the crossfire cables when you switch to gaming mode.

The sapphire vapor cards seem to be the best for hashing... Agree/disagree?

Good to know. Yeah I might hook up the cables when I want to show off benchmark scores or a bit of gaming

Edit: how many kh/s do your gigabytes get?

I don't like 7950s for two reasons. 1) because you have to run them at intensity 20, they draw more electricity than 7970s. 2)because of high intensity, I found them to be less stable and not as efficient as popular consensus claims.  Moreover, I had the standard Sapphire 7950s (the ones advertised on coinchoose), and those fans are as loud as a industrial vacuum cleaner.  So, if you don't have a basement or garage, or just some separate space for your rig, then it can get really annoying.  I have twelve 7970s, both Gigabyte and Sapphire Vapor-X.  The Vapor-X are awesome and seem to be most stable.  That's not to say the Giga's are bad.  It's just that the Vapor-X gpus have worked pretty much flawlessly.  The Giga's have had a couple hiccups along the way, but nothing serious.  But the Giga's were $400 usd from Amazon and I'm a prime member and I get 764kh on them.  The Vapor-X were $450 and I also get 764kh on them.  A quad rig pulls 1300 watts, without touching voltage. 

-Merc

Don't even try linux for a mining Scrypt unless you are either very competent with Linux already or have a 150+ IQ.

I don't like 7950s for two reasons. 1) because you have to run them at intensity 20, they draw more electricity than 7970s. 2)because of high intensity, I found them to be less stable and not as efficient as popular consensus claims.  Moreover, I had the standard Sapphire 7950s (the ones advertised on coinchoose), and those fans are as loud as a industrial vacuum cleaner.  So, if you don't have a basement or garage, or just some separate space for your rig, then it can get really annoying.  I have twelve 7970s, both Gigabyte and Sapphire Vapor-X.  The Vapor-X are awesome and seem to be most stable.  That's not to say the Giga's are bad.  It's just that the Vapor-X gpus have worked pretty much flawlessly.  The Giga's have had a couple hiccups along the way, but nothing serious.  But the Giga's were $400 usd from Amazon and I'm a prime member and I get 764kh on them.  The Vapor-X were $450 and I also get 764kh on them.  A quad rig pulls 1300 watts, without touching voltage. 

-Merc

I was originally thinking of 7970s, but they draw more power : fact. A 5x7970 rig would require more than 1475w like my 5x 7950 build

I forgot to mention resale value of 7970s are much better.  This is going to come into play when next gen models hit the market later this year (supposedly).

I forgot to mention resale value of 7970s are much better.  This is going to come into play when next gen models hit the market later this year (supposedly).

Why is it difficult to mine with? Also what am3/ am3+ board would you recommend for use with risers?

990FXA-UD5 board you might find for 100.00 USD and supports 5 gpus without having to short out the pcie slots.

As for the GPUs I would suggest either MSI R7950s REV 1.0 8pin 6pin (not hardware locked) or Gigalock cards flashed to F43 BIOS or you will be stuck with a hardware locked voltage of 1.250v.  :o

4,000KH/s is not going to get you many LTC these days, you would be better off mining DGC and other ALT coins.

This site is helpful for determining what coins to mine.
http://www.coinwarz.com/

I'd invest a bit in the CPUs as well (the more cores the better).  If you're building a mining ring you might as well get the best CPUs you can as well so you can swap over to any new coin that catches your eye and not worry about if it's better to mine said coin with cpu or gpu.

You could also cpu mine primecoin VERY efficiently while mining your LTCs.

I'd rather invest in Gpus than CPUs, how profitable is prime coin

It's not profitable (unless price/demand goes up), but LTC is in that same boat right now too.  Right now an alt coin mining rig would really just be a way to crank out some hashes on promising new alt coins.  It likely won't be profitable as a pure LTC rig unless their value goes up.  

If LTC is all you want then buying $4k worth of LTC might be the better way to go.  (look at it this way:  for $4k you could buy 1,333 coins, or you can spend 300 days mining 1,333 coins (don't forget cost of electricity)).  It would take 10 months or so at current $ values (+ difficulty) to break even on your proposed rig (not including electricity, it adds up FAST for GPU rigs).

I'd rather invest in Gpus than CPUs, how profitable is prime coin

If you had jumped early on with a few i5 or i7, would have earned triple-quad digits in the first few days :)
Builds are okay imo  ;)