Your oem t/b or c/b is sufficient for the change in boost. The GTI oem is 2-3/8" and the R32 oem is the same diameter. All tests and write-ups I read for the first three years we had the mkv, nobody ever showed a hp gain with an exhaust mod after a remap. There were many shops modding to stage 2 and they would all dyno the cars: stock, with an intake, after remap, and finally after a turbo back. The reports were all the same showing the same hp after a remap as they did when the exhaust was added afterward. The one you are looking at should be sufficient. They will tell you you need a dp, but you don't. I ran a stage 2 remap with the oem t/b and it ran 14.1 et's at 100mph with an intake and remap. I eventually upgraded when I installed my K04, but only up to a 2.5" t/b. Whether or not the R32 c/b is going to fit the gti dp perfectly...I couldn't tell you.