I know how this feels. There's always a car with 100bhp more. I'm quite happy with mine at 270bhp but I'm definitely going k04 at some point. However I just know that I'll get used to that, and so it goes on and on. I went out in Hurdy's R when it was running 500+. Made mine feel very tame.
I reckon the trick is to drive a 'normal' car as much as you can. Then the GTI actually feels quite quick when you get back in it!