Is my x58 mobo a bottleneck, too?

[Taegan The Zombie]

Up until now my gaming computer could handle whatever I threw at it, but recently I started playing GTA 5 for pc. I know that my HD5850 is the main problem (notably the 1gb vram), and I have looked around and think my best bet is a r9 290 off Newegg (I'm partial to xfx for their oc warranty) for roughly $250. Then I started to wonder if my motherboard was outdated, as well? I'm fairly certain my CPU is powerful enough, but I could also be wrong there. Another thought is how much would I benifet from upgrading from 6gb to 8gb ram, or more?

Here is my build:
EVGA X58 FTW3
XFX HD5850
Intel i7 930 @2.8GHz (with cooler master v6)
6gb ram (3x2gb) ddr3 1600, 1.65v, latency 7
NZXT Hale90 1000w psu
150gb velociraptor
2tb wd black
Red & black HAF case


And after upgrading to the XFX r9 290 ($250) what would be the weakest link as far as playing GTA 5 on the highest settings I can and still get ~60fps @ 1080? Thanks.

Edit: I can also just get a 5870 for $120 locally, but I don't think a 5850 and 5870 in Xfire will give me as much as a r9 290, right?

 

[Taegan The Zombie]

"No stupid questions" doesn't apply here?