I believe that Tri-SLI scales better than Quad SLI. Although both are going to have high power consumption and be great GPUs. I say you should go with another GTX 285 and run Tri-SLI.
Originally Posted by 003
1. 3x GTX 285 beats 2x GTX 295. It's 3 faster GPUs vs 4 slower GPUs, and since it's only 3 GPUs, the scaling is better as well, and less micro stutter. This is a no brainer. This has been tested a number of times, you can look it up. 3x GTX280 also beats 2x GTX295.
2. No, you don't need a bigger PSU. Your PSU is already more than enough.