ausracer: The G2 has different front suspension from the G3.
The G3 has and extra bar mounted across the front suspension, I'm not totally sure if that is all but other than that they look pretty much the same to me.
I don't know about asphalt but they're still competitive on carpet, they are also very tough which could be useful if you're going to be racing 6 cell mod
Here's a pic of a G3, you can see the thin bar joining the suspension, probably for less roll.
(I'll try and post a pic of my G2 later)