I've just changed mine to 256mm rears, when people say you have to use 2wd calipers its a load of crap as the 2wd and 4wd clipers are excatly the same part....its the carrier that denotes weather of not you need a 6mm spacer.
Any mk4 platform 256mm calipers so you have a choice of CupraR, 225bhp TT, S3, Octavia VRS, Golf R32, Golf 4motion etc.
The carriers will bolt straight on if there 2wd but if there 4wd you need a 6mm spacer and longer bolts.
The bolts are Not M8 as most people will tell you there Metric Fine [I paid £2 for 4 that were 10mm longer then standard, high tensile]
For spacers I bougt a small sheet of 6mm steel and cut my own [cost £5 and I got enough material to make 4 sets/8 calipers worth]
Make sure you threadlock the bolts.
The pads for the 232 and 256mm discs are the same to.
pics for comparison