If the PSU is 900W, you don't need it, even if you're running SLI. A single high-end video card setup typically needs about 250W tops, so a 500W-600W PSU is fine. Add about 150W per high-end video card you add.
I'm tempted to say, you don't need the secondary SSD either. Load times across mediums are hit and miss with games. And it depends on how much you care about load times anyway. You might also get a slight performance boost on games that stream data, but I think the last time someone tried to pass this off as a "reason to buy SSDs", there was an FPS difference of single digits at best.