For a short time (1-2 weeks) it may be OK, the cards are rated to 95c. The fans do not do well at temperatures like that, and will be the first thing to fail. Unfortunately, you'll just have to make a call. Is it worth the extra wear and tear on 2 cards for an extra 700kh/s for two weeks?
The cards should be OK running in a really cold room. I would try and stay above freezing, though. If it is a small room it will not take much time at all for it to be really, really hot! Prepare to be amazed!
yes i totally got u. really thank you. i m not ok in english and im also newbie about mining. that advices will prevent me from bad things.
i will run with two x16 3.0slot at first.
i also got two of 5970 cards but i will keep them for my future second rig or i will buy 1500w psu and run with 7 gpu but im not sure it will be safe or not.
5 gpus per rig, seems more safety for working.
No problem, glad to help. Your English is pretty good actually.
Well, the thing to watch for is the input power. Here in USA line voltage is 110V, and a home circuit rated for 15A. Therefore, if you want any more than ~1500W input power you have to worry about home wiring being too small. This limits most US setups to 4 or 5 cards, especially 250W cards like these.
If your home circuits are 220V at 10A you have much more capacity than us Americans @ 2200W. You could then theoretically run more than 1500W on one circuit (Please check this yourself, I don't know your area!) Maybe one 1500W PSU and one additional cheap one, for 7 cards one one circuit breaker.
I have never tried, but I have hear mixing GPU series (59xx+79xx/280x) on one computer can be hard sometimes. I can't help here, sorry!