I live in Brazil, PC parts here are ridiculously expensive, but I'm going to north america(US and canada) next month, and I'm planning a $1000 upgrade.
I have 3 22 inch monitors, running games on 5760x1080, right now, I can run most new games(BF3, fc3) on medium, but I'm focusig on a machine able to max out most modern games( Anti aliasing included).
Right now I have:
Don't spend 350 on another 6950, they weren't that much new. If you can't find one for under $200 then you 350 is best spent on a 7970. Or better yet, sell your 6950 in Brazil (sounds like you'll get more for it), and buy two cards with the extra money here (not sure how much you'll end up with).
The 650W will be fine.
Look at the "Best SSD for the Money" on this site for recommendations based on your budget.
It should handling it under the no oc scenario. As for the 6950, and computer parts in general, stores here typically have poor selection at high prices (apart from sales and specialty warehouse stores) and internet is almost always better. The 6950 is pretty scarce now I wouldn't expect much luck other than 2nd hand.