well if the OP is still wondering whether or not the mentioned rig will be able to play GTA 5 or not,let me confirm that i am 110% sure you will be able to play it.....just not sure on which settings
Seriously though,on the rig mentioned in my profile which i3 2100 and GTX 460 SC (a lil better then 6850) i have played dozens of games including Battlefield 3 @ 1920x1080 and ALL settings on Ultra including AA i got 35 FPS on average. And if you did not know,BF3 is one of those games that requires a LOT of juice to run normally.
What i mean,i can confirm from personal experience,no matter how good GTA 5 looks,your system will be able to play it on at LEAST medium settings.
I suggest you simply upgrade your GPU to7850 or if not then a 6950/6970 so you can be sure to play the game on at least High settings.