Interesting discussions in here
Ive owned 4 106GTi's tuned to varying degree's and im not in ownership of my 1st ph2 172, and i can say there isn't alot really between them.
First of all the 172 is quicker hands down, yes up to 30, 100 or 130 whatever, however id say the GTi handles that little more so better, however I would like to point out ive seen many a VTS/106GTi run low 15's on pod days, and infact my first 106GTi pulled a 15.3 when it was 100% standard, since then ive rarely seen a 172 in standard form get much quicker than this really, certainly not enough to warrant the term 'tanked' anyway.
Mods on a GTi are leathal... my 2nd one remapped, decat, full system, manifold etc, seen a sub 15 standing quater, and could easily hold its own against 172's ph1 and ph2, id really wish it was still kicking around as id be interested to see if it's quicker than my clio
End of the day its horses and courses, personally theres very little in each, 172 quicker ever so slightly, but a couple of choice mods and the 106gti is more than a worth oponent