What suggestions do you mean specifically with the next question? Either gpu or psu?
gevinn :
Any other suggestions are welcome, thanks!
With these gpu's i assume you are looking at second hand ones....
The psu has 300watts on the 12volt rail so in theory it should probably run either card with the rest of that system,
but in practice i probably am only comfortabel with recommending the hd 6850.
The thing is that the hd 6950 is quite a bit better then the 6850.
You could just try it out,but that's totally up to you.You will have only yourself to blame if things might go wrong!
With the 6950 you would also need a molex->pcie adapter because your psu only has one pcie connector of it's own which would be enough for the 6850,but not for the 6950.
With the 6950 in the end it probably would be better to buy a good psu with it,for example a corsair cx builder 500watt which isn't the most expensive and has the 2xpcie connectors.
Again with this psu i'm only comfortable recommending the hd 6850.,but in the end it's up to you and your budget