Actually the back end is not very playful at all, it is very very secure. Even flicking the steering wheel and backing off at the same time does nothing. At the limit, there is a little understeer, but to get to that point I'm already having to go faster than I dare!
Basically suspension spec is:
Powerflex front upper wishbone bushes
Eibach anti roll bars front & rear
50mm overall wider track due to wheels (vs std 156 on 16" rims)
My GTA is more playful with the back end, on my GTA I have the following:
Eibach shocks & springs
Original 156 GTA front anti roll bar with Powerflex bushes
Eibach rear anti-roll bar with Powerflex bushes
Standard GTA track which is 37mm more than an original 156 on 16" wheels
Standard GTA alignment settings
I think its the stiffened rear anti-roll bar that is making the GTA more oversteer-biased rather than understeer-biased. I'm happy with both cars as they are, its nice that they are different.