As someone who had a Stage III 500 and now has a 3 door running a T34 with Greens, 500 cooler etc etc etc
I would much rather have the 3 door as a car to drive on a regular basis.
I didnt find lag too much of a problem with the 500, but then I had it set up by Bob Murray at Automotive Unlimited who rejetted the amal valve and used a decent chip designed for the 500 running greens.
To drive on a track I think the 500 would be harder work because you'd have to keep the revs up to keep on the edge of the turbos 'power band' ie around 3750 rpm ready for when you come out a bend and nail it up the straight.
Would I have another 500......... ?? Errrrrrrr go on then...