Sorry mate, but its gonna be really, really hard to find a PC running GTA great at all times.
To me, the game sounds worse than Crysis, but not because it graphicly intensive, as much as because its coded like crap.
I wouldn't advice you to go out and buy a Quad to play GTA, if it helps at all, it only helps a little.
Just live with the tiny lag, your system should be ok, playing most of the time.