Right before I sold mine in favor of 7970's, I was pulling down +/- 1btc a day out of 2. One was on water, massive overclock, the other was on air, not-so-massive overclock. My electricity is 6.9c/kwh, at current prices I was making right around $4.change a day, paying them off in 6 months. If you can get a couple for under 350, maybe some xfx's that have the second lifetime warranty available, I'd say go for it. They are sort of, well, prone to failure so figure that in to your overhead, and it might make more sense to get newer generation cards.
7970 will drop in value fast. Even at 7c electricity I don't see the wisdom in purchasing a 7970 solely for mining (would have to have some gaming on the side). Maybe if the electricity was free.
I had seven 5830's that I bought for $110 each..... but also got a steam key for Shogun 2 download... which sold for $10-$15... So, about 95-$100 for each 5830. A year later, I've sold all but one of those... total depreciation? Well, nothing..
7970 a year from now will be worth much less. 5970 is getting close to a good buy point.... Another couple months should see them under $300, probably around $275.
Right now? 5830 (or 5850) is probably still the easiest to get at a price that won't drop much in absolute $... but 5870 might be the best value when you figure in hash rate & efficiency. 5870's are what I've been buying, price point at $160 or less (a little higher for XFX).
I think most people just choose to ignore their equipment depreciating in value when figuring profit..
Sorry, but I'm going to have to agree with the crowd on this one. 58xx prices have been artificially inflated by the mining market for over a year now. The technology inside the cards is almost 3 years old now. Granted the cards game pretty decently, you can find a much better card for playing games at the same price range (5870 ~ $150). Which means not even gamers will want the 58xx cards when the miners are done with them. However, 7970's will still be very good cards for gaming, even if at a discount. The point is, the current and previous returns you've made on 58xx cards are completely negligible because gpu mining was still profitable when you sold the cards. I honestly see the last string of 58xx cards selling near the $50 point. Which, since you mentioned percentages, is actually a larger loss than a $350 7970 (and who actually pays $500 for a new 7970 anyway?).
