I believe it's too late in the game for GPU unless the price of BTC skyrockets another 100% from current prices ($150)...
I agree with you about the ASIC having a single purpose, however, GPUs will have a single purpose soon as ASIC gets deployed.
The only reason I keep mining is because it's profitable for me since I already paid for my GPUs and rigs a while back, especially at the current BTC prices.
Makes little to no sense to invest $1700 in a rig that won't get a return of investment anytime soon.
At the most, you'll be mining 3.5 GHash per Rig (given you install 4 high end GPUs such as 7990's) and even then, that's a $4000 rig easily and you'll be making 0.30 BTC a day 9 BTC per month at current price/difficulty you're looking at 6 months ROI and that if if the difficulty remains the same, which it certainly won't after ASIC is fully deployed... so maybe you'll have an ROI of a year or more...
the 7990's you can't get them for less than $800 and I don't see ANYONE selling an used high end top of the line card for any other reason than being broke and needing the money or to buy drugs! LOL
I totally disagree with you. The ROI of such a machine would be perhaps 2 month or so. You have to take into account that, unlike ASICS, these GPU Miners are not a one-way investment. Yes you are right: You spend 4000 Bucks for hardware. If you make 9 BTC in the first month, you would have around 1500 bucks at the current price. Even if you need to month for that goal, you can easily sell these cards to other miners or, what is more important, gamers. There are always enthusiasts who pay 80% of the original price for used GPUs. So you would get around 3000 Bucks from your 4000$ investment. That makes it profitable very soon. And from that break even point you can decide each time to sell the hardware. Luckily bitcoin mining is actually much faster than decrease of your hardware value.
Just my 2 cents.
KJ