Eth mining video card question

[molitar]

I have an Sapphire Vapor-X R9 280X Tri card which is overclocked to 1070/1550.  I use my system mainly to browse net and watch videos so I started to mine Eth as I usually do not play many games that require me to shut it off and my PC never gets turned off.  I am going to pick up a second GPU and my choices I have found are.

R9 280X 3GB OC  $280.00
R9 380X  4GB OC $230.00
R9 290X  8GB       $340.00

Which GPU would be my best bet?

[ZipEyes]

I would pick 280x for myself.

[adaseb]

Buy a used 7950/7970/280X, don't buy new.

[molitar]

Used is the same damn price as new pretty much anymore.  When I bought my 280X new it did not cost what it cost now even used!  Since these miners put the card in demand the price has jumped up!  I have looked all over used $229.00 I rather spend the $50 more dollars and have a warranty and know the card is good. I found one card for $150 on craigslist and already gone because I got to reply back.. these cards sell too fast.

But I guess I am misunderstanding what is important for the hash rate?  I thought a big part of it was the memory size but since the 8GB has not been recommended I guess I was wrong.  The other thing is I am running a card that has boost at 1000Mhz already and so if I am going to get a 280x I am going to get another 1000Mhz card. So I'm not going to go to a lesser card since it is also used for my personal use at times.  If it was just for a mining rig only than the price would also be a big concern.  Right now I rather worry right now about power requirement and hash power of the card over everything else.  If one card hashes pretty much the same but has better power requirement than it's worth the little extra to me.  So if that is the 280X at $280.00 vs the 380x card than that is what I will do. 

[JuanHungLo]

Get the 280x.  Undervolt both cards to 0.95v, if stable, lower your clocks and memory speed to 875/1250.  Sit back and make $4.16/day/GPU before electricity costs.

[molitar]

Get the 280x.  Undervolt both cards to 0.95v, if stable, lower your clocks and memory speed to 875/1250.  Sit back and make $4.16/day/GPU before electricity costs.

Thanks so it's the undervolt that allows better ROI.   I just got a used one from Craigslist the XFX DD which is overclocked to 1080/1550 MHz for $180.00 so not bad at all.

[JuanHungLo]

Get the 280x.  Undervolt both cards to 0.95v, if stable, lower your clocks and memory speed to 875/1250.  Sit back and make $4.16/day/GPU before electricity costs.

Thanks so it's the undervolt that allows better ROI.   I just got a used one from Craigslist the XFX DD which is overclocked to 1080/1550 MHz for $180.00 so not bad at all.

Well undervolting will spare the electric bill.  My experience with the XFX 280X DDs is that you shouldn't attempt to undervolt lower than 1.125v or they freeze forcing a reboot.  Still they are great cards with lifetime cooler replacements via RMA online.

[molitar]

Get the 280x.  Undervolt both cards to 0.95v, if stable, lower your clocks and memory speed to 875/1250.  Sit back and make $4.16/day/GPU before electricity costs.

Thanks so it's the undervolt that allows better ROI.   I just got a used one from Craigslist the XFX DD which is overclocked to 1080/1550 MHz for $180.00 so not bad at all.

Well undervolting will spare the electric bill.  My experience with the XFX 280X DDs is that you shouldn't attempt to undervolt lower than 1.125v or they freeze forcing a reboot.  Still they are great cards with lifetime cooler replacements via RMA online.

Thanks but I underclocked and undervolted this Saphire R9 280x video card and my wattage still reports as 485-500 Watts from the UPS load. So really I don't see any change at all from the load at the APC level.  So where are people getting that this saves money?  Temperature is about the same also so I don't see a need to do this at all.  

Trixx utility set to 875/1250/950 vs default 1000/1550/1250