Are 7950/7970s still worth the price? And can gigabyte motherboards run (x)GPUs?

[zeuzzz]

Noticed that the availability of these GPUs has all but vanished from most major suppliers, and most of what we have is ebay and other user based market listing left. The average in the UK seems to be £350 per GPU, since it's being touted everywhere as the best low power for high hash rate card (and rightly so).

However as I'm upgrading my entire computer set up anyway and plan to buy 3-5 GPUs over the next year for it it's got me wondering if there are cards that are nearly as efficient at mining that are not as hyped and so are not as costly? Forking out £1000 for 3 GPUs seems like a bit much, or are they really worth their current value?

Also as a small secondary question, I have to run OSX on my PC as my uni course uses some software that is exclusively Mac (Logic Pro) and I've had a successful hackintosh running 10.8 Mountain Lion now for two years on these specs:

System:
    GA-Z77X-UD5H [rev 1.0]
CPU:
    Intel Core i7 3770 3.4GHz Socket 1155 8MB Cache
Graphics:
    Gigabyte GTX 560Ti OC 1GB GDDR5 Dual DVI Mini HDMI Out PCI-E

My trusty lil GTX runs away at 140 khs with cudaminer and the correct config settings, in windows or OSX. However since many motherboards are not very OSX friendly gigabyte seems to be the boards with by far the best native support for running OSX (my GTX GPU also runs natively with no MAC drivers needed!) so is there a gigabyte motherboard that I could buy for my next upgrade that would allow the attaching of 3-6 GPUs in anyway? I presume this is impossible with my current board.

I'm still kind of n00b about the whole multiple GPUs on one computer thingy. Thanks.

[repairguy]

Your motherboard can operate up to 6gpus (assuming that all the slots are usable at the same time)

With good cooling and overclocking a 7950 can run 600-700khs

I have had alot of trouble with 7950's but there are alot of people who love them and make them scream.

I can make no comment about mining on osx, I have never done it and dont ever intend to.

At current litecoin price and difficulty if you can make a 7950 run 700khs it will produce 4.07 a day in ltc.  If you also game with the machine the 7950 is a pretty badass card.

[zeuzzz]

Will my mobo and PSU be able to hack a 7990? I'm thinking of just biting the bullet and getting one of them. I've a TX750M corsair running the above CPU mobo and GPU, would it be a good idea to get an entirely new PSU for a 7990 and can anyone recommend the rough wattage increase I would need to power a 7990?

[repairguy]

The sheet I have says the minimum power supply for a 7990 is 700watt. Amd's website says 750watt. Corsair is a quality supply so It should be able to handle it.