The shell material is better?Yeh, without a doubt, no sane manufacturer would shoot themselves in a foot. Not when ie900 is already a massive hit. I did have some issues with ie900 tuning and i think ie600 remedies that for my preferences. i would not expect it to be technically superior though.
The overall tuning is a more mainstream one, so the total performance is very similar.
it’s like the Honda S2000/FD2 faster than the nsx (old)… but the nsx remain flagship…