I had the 16V XSI (basically the S16 as was) and a GTI-6.
The GTi 6 was quicker but i preferred the XSI. It did everything very well without being too stiffly sprung. It did roll a bit too much tho.
Loads of problems with it though.
Id put the GTI in about late 6s early 7s to 60, and the XSI about 7.5 to 8. (never timed them though).