Lots of good points made here.
@Pudding Have a look at Dan's build here, he's fitted a k03 hybrid turbo with good results. Well north of 300bhp, safely, and minimising lag:
http://www.mk5golfgti.co.uk/forum/index.php?topic=88732.msg1002464.msg#1002464I was well aware of the potential of an ed30 before I got my k03 GTI, but I just couldn't stretch the budget enough to get a good one.
Yes, I have spent a bit on BBS VZs, ed30 front, colour coding etc, but even taking that into account I think I'd still be a bit short of proper eddy money.
I like the k03 for what it is. It's never going to be a straight line monster, but on the right road it's so good to drive, especially with a bit of R-Tech magic.
I think if I really wanted to do the k04 (and inevitably beyond) thing, it'd make much more sense to me to go 4wd and DSG.
After going out in Hurdy's 6R, even though it's an extreme example, I can't help thinking much more than 350bhp would be wasted on a 2wd car.