Which is a better value?

6850 or 7770?

I'm limited to these cards because of my budget and 400w psu.

The 6850 after MIR is $125

The 7770 after MIR is $110

I'm wondering if the more powerful 6850 is worth the extra $15. Especially as far as Guild Wars 2 is concerned.

Computer specs:

i3 2100 psu
4 gig 1333 ram
1tb Spinpoint F3 hdd
400w Corsair psu

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

http://www.amazon.com/HIS-Radeon-Eyefinity-DisplayPort-...