Nick, I disagree with your statement about the GT2 being unstable.
I used mine for a year, did almost 20000 kms and 8 track days with it, and I can assure you that it's not unstable.

Grant:
Sorry for answering so late.
To put in the GT3 in the Modena vs GT2 comparison is tricky.
The GT3 I would say is a little bit less quick than a 360 in a straight line (actually very little), it has very good traction like the GT2, it feels nimble almost like a 360 but it is less quick on turn in.All in all I think the GT3 is an extremely good car, but I have to agree with RC on the fact that it needs to be modified to really be effective on track.