Thinking about getting a new GFX card

...And I was wanting to check this would work. for the most part, I'm fine with computers, but I hate missing something and then having to deal with sales because of a stupid incompatibility.

I'm running:
Corsair VX 550w
Asus P7P55D-E LX
3.2GHz i3 550
2x 2GB Corsair DDR3 XMS3

Would a Saphire Radeon HD 6850 1GB GDDR5 Toxic edition run?
Is it worth the step up from my Radeon HD5670?
The card claims to require a 500w PSU, but I'm wondering if my rig is otherwise drawing too much power? That's the only thing I can initially think of going wrong, but as I said, I hate missing stuff.

Personally, I'd get a new CPU over a GPU. The i3 series are all dualcores iirc.

If the card says it needs to have 500w, you should be fine as that's calculated along with a normal build.