Folks,
I'll add my comments on larger front brakes. I've got several mkIV series VWs. One of my parts cars is a Jetta 1.8T. I was getting ready to do struts on my 2005 Beetle and figured I'd pull the entire knuckle/strut assembly and swap it out.
I pulled the knuckles off the 1.8T parts car. Removed the old struts; removed the old wheel bearings; removed the old lower ball joint; removed the rotor, calipler and caliper bracket. The caliper bracket is removable on the 1.8T knuckle and the Audi TT knuckle. I picked up a set of front calipers and caliper brackets for a mk1 Audi TT (the calipers are the same as the VW 1.8T) for $100 from ebay. The Audi TT has 312mm front rotors. Pressed in new wheel bearings; installed a new lower ball joint; installed new struts; mounted the Audi TT caliper bracket.
On my Beetle, I pulled the whole strut/knuckle/rotor/caliper assembly and replaced it with the 1.8T knuckle with all new parts and the Audi TT caliper bracket. Installed new 312 mm front rotors and new pads. Replaced the TDI front calipers with the Audi TT/1.8T calipers and bled the brakes with my motive brake bleeder. Once everything was back together I took the car in for an alignment (since I put new lower ball joints on).
One thing I notice is the steering is much "firmer". By that I mean when I turn the wheel, the front end doesn't seem as "light". I'm guessing this is due to the heavier/larger rotor and calipers.
Eric