No, the Corsair 650w is an excellent psu.
The 6850 will run on a 500w psu:http://www.amd.com/us/products/desktop/graphics/amd-radeon-hd-6000/hd-6850/pages/amd-radeon-hd-6850-overview.aspx#3
Adding a second will take less than 150w extra.
It looks like your interest is gaming, so I think you should re-evaluate your plan.
Bulldozer was a disappointment for gamers, check out some FX-8150 reviews. Your X4 925 is about as good.
On Tom's most recent list of the best gaming cpu's for the money, there are no AMD chips in any price category.http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106.html
Since you are thinking of a motherboard change, why not go with a Z77 based motherboard and a sandy/ivy bridge cpu of some sort?