As my previous car was a 25 Gti, I decided to get a ZR 160 more because of the way it looked as I didn't think the drive could be much different. How wrong I was!!! I think the ZR handles much better with the ride being much firmer. Currently only done 800 miles in the ZR but you can already feel the difference in the acceleration.
I have driven all 4 of the cars you mention (only ever owned the 25GTi though). In order that I drove them to give some feel for the progression of thoughts...
200Vi: Found the 2 Vi's I drove to suffer terribly from torque steer, to the point where I was lifting off even when in a straight line! Reasonable grip and speed, quite enjoyed the drive with exception of the torque steer.
BRM: Didn't drive it for long but found the suspension very hard. Otherwise very quick and excellent grip.
25GTi: Very quick, handles well - brakes need a little more bite, they fade too quickly (although a set of EBC Green Stuff pads seem to have solved that one). Eats front tyres (or is that just the roundabouts in Milton Keynes? ) but well worth it.
ZR160: Have to concur with previous comments - didn't think it would (or could) be much better than the GTi, but have to confess the grip felt far better than I was expecting. Can't really comment on power differences, the ZR had less than 1k miles on the clock and the dealer asked me to be nice to it!
Was looking to buy a 200Vi, but got an MGF instead at the time. Would love to 'upgrade' to the ZR160 but can't afford to. More than happy with the GTi.
Hope this is kinda what you wanted, if you want me to bore you with more detail let me know...