Two lower end GPU's in SLI vs. one higher end GPU.

Have to be honest, up until today, the usage of a single card was more stable than using it in SLI/Crossfire, both Nvidia and AMD have improved their solutions, both in software and hardware, in order to provide a more reliable multi-GPU usage, therefore it is expected to SLI/Crossfire to run stable more and more frequently. Another point would be that the newest usually are built with newer technology which may be capable of getting better quality graphics, with less heat/power usage, but if you do take this in a huge regard, you will always wait for something, and will never get it.

I had not sought out for it, if I were you I would check several things before going SLI, such as:

- Is your motherboard compatible to it ?
- Is your PSU ready to provide the power needed to your system if running it on SLI ?
- Do this model have any known big issues when SLI'ing it ?
- What is the common scaling performance from a single card to two of them ?

I for an instance, I already have a GTX760, and I am planning to get another one in the future (as soon as Nvidia/Ubisoft start to bundle Watchdogs to it - really hoping it happens), there is already information on the web about Nvidia "Maxwell", which should substitute the actual "Keppler" used on the 700 series, and that the 800 series would be built on it. That does not mean that my system will become outdated and needing an update. It only means that there is already something out there that is newer and built with different technology, the same will happen when the 900 series come out, the 1000 series (or whatever they want to call it).

With all of that said, I really believe that at this point, 2x GTX 660 will reach the performance you want for a good price. Whenever that becomes old and really outdated, than maybe a full upgrade (or another rig, who knows?) would be a better option than the change of a VGA.

Hope it helped.

Update: As referenced, not all games support SLI/Crossfire at this moment, but that number is increasing daily, and in the (really) close future that should be the "standard" as well as multi-core CPU usage.