I've started mining with a small rig. I've picked up a couple of used 7970's. I'm running ubuntu 12.04 with cgminer.
I actually, don't know that much about the cards I bought. One is a single fan 7970 that takes up 2 slots. The other is a 2 fan unit that takes up 3 slots. Call 'em card 0 and card 1.
I start cgminer with the auto fan option.
Card 0: 1185 Mhz CPU, 1035Mhz Mem Clock, 85% fan, 74C
Card 1: 1185 Mhz CPU, 1035Mhz Mem Clock, 35% fan, 72C
Both are generating 706Mh/s.
Sweet!, But I think it's a bit hot. So I think - kick up the fan on Card 1 (85%) and maybe that'll dissipate some of the heat from Card 0.
Now: Card 0 is 68C; Card 1 is 59C
But Card 0 is doing 650Mh/s, Card 1 is doing 706 Mh/s.
Could/Does the temperature affect the hash rate?
i don't know about 7970's specifically, but ppl tend to give figures way too low for "safe" temps (esp on overclocking sites)
if the 7970 is anything like a 5830, 5850, 5870, 80o (or probably even 85o) or lower for the GPU is fine.. as long as all GPU sensors are below 85-90o and all VRMs are below 100 (well, these I think are fine up to 110-120, but...)
until about two months ago, i kept all my cards below 70o. but not really possible now in this heat. i'm in texas and the comps are in a sealed off room, it's well-ventilated but temps still get to be about 5-10o above outside temp. so if it's 100o outside, it's 110o in there. it's cooled down a bit lately, but back when the outside temps were 105o, i'd have a few cards that would get close to 80oC during the day, lately they've been topping out around 75o...
a lot of times if you have old thermal paste on there or someone gunked it on there, what you see as your main GPU temp could be rather misleading. there have been several cards I've gotten off of eBay that'll read 70oC but have gpu 3 sensor at 90 or 95oC. that's not good, it usually means 'take this pos apart and re-apply some thermal paste', on rare occasions it means 'take off this pos fan and shroud and ziptie a super-loud badass 120mm fan on this mofo'. i have one of the latter. i put it at the bottom of my stack since it takes up 3 slots w/ this massive 120mm fan, but it keeps the middle card a lot cooler too.