s4 rear disks are 300mm I think that's the most common upgrade.

 

4 pot brembo porsche calipers will brake better. You can fit 300 mm rear discs and keep the standard caliper if you have a mk4 . I don`t know of anyone fitting a bigger caliper but if you do your make the braking even worse by doing so.

 

also ecs do this kit which is straight bolt on and means you keep the use of your handbrake. More expensive though

http://www.venommotorsport.com/brakes/ecs/stage-1-big-brake-kits-rear/vw-golf-mk4/

 

I got a set of pre drilled 300 mm discs but have run out of the brackets needed to position the caliper as i used to sell 300 mm rear rear brake kits but nobody seemed interested so didn`t make any more after the first batch.
http://www.r32oc.com/topic/144017-mk4-r32audi-tt-300mm-rear-brake-discs-and-adapters/

 

No scene points for standard looking upgrades!

 

so if i was to buy brembo 4 pot porsche calipers what discs could i use? the standard ones?

 

Yes with the correct adaptors. Your brake master cylinder only holds so much oil ( cannot remember what at the moment ) so calipers that use more oil then OEM you get less brake pad pressure on the discs and a spongy peddle feel.

 

Take your pick

http://pages.ebay.com/link/?nav=item.view&alt=web&id=221756520380&globalID=EBAY-GB

http://pages.ebay.com/link/?nav=item.view&alt=web&id=321735613652&globalID=EBAY-GB

 

Take your pick

http://pages.ebay.co...lobalID=EBAY-GB

http://pages.ebay.co...lobalID=EBAY-GB

I don`t think it is possible to fit 355mm discs to the rear of a Mk4 and keep the hand break as 300m-310mm is a tight fit and a bitch to get the handbrake cable on.

 

The handbrake is mounted the opposite side to usual so may work