mk1s and 2s are done for a reason blue, they are light, agile and have the right posture and handeling for a track car. Mk3s are too lardy and you need to invest far more into them to get the same gains as you would get out of a mk1/2 for half the price.
I would say mk1, with a mk2 16v engine, on throttle bodies, or ported and polished, balanced and lightened fly should see you with nearly 200bhp at the fly, and 165-170 atw no problems.