I don't think even an Mk2 GTI 16V (hard roof) would beat the ST as it was slower than my 16V Clio which has Identical performance to the ST. The Mk3 16V was even slower due to the added weight. As for the Mk1 it did not exist in 16V (only 8V 112 bhp) so similar to a Mk 3 Cab. In other words thay are all slower than your ST - for anything faster you'd have to go for a VR6.

OK just thinking about it, maybe a G60 might be as quick (the 2WD, not the Rally) provided it's well driven but the gear changing on the G60 was VW's first attempt at using cables vs. rods in the shifting and it was extremely cumbersome and slow resulting in a 16V (which used rods) being faster despite having 22 bhp less and weighing about the same.