The 18x8 Ultraleggeras that the TireRack has would work for GS at $335 each, their offset is within the 1/4" allowed (aka 6mm). If one of the VW rims for the GTI MKV is 17x8, the 17x8 Ultraleggeras the TireRack sells for $265 would also work. I honestly think I can find a rim at the cost I want to pay. I will likely end up buying the the 17x8 Flik Ftd's from EdgeRacing.com and run them with 245/40-17 tires in STX. As they have matte black rims for $79 a rim and matte titanium for $99 a rim, each weighs 18.5 lbs.
I have been researching this as well, and I really wish I could find a 16x7 rims that is the correct offset. As the 2007 MKV GTI can be shipped from the factory with 16x7 Tangis rims. EdgeRacing sells some 16x7 Flik Ftds that are $89 each but the offset is 33mm and the Tangis is 50mm.
The advantage to 16" rims is it lowers the car (assuming to mount a low profile tire on it) and also gives you a mechanical grip advantage with a smaller overall diameter. This can be achieved a little with 17x8 rim and 245/40-17 tire which drops the car by 1/4 to 1/3 an inch.