The horsepower is largely irrelevant.
Here's an analogy: An Edition 30 running 320bhp on the standard downpipe, cat and exhaust. So the oem exhaust is a good solution, right? No. EGTs are through the roof and the turbo is being forced to work its bollocks off.
My last word on this. I knew pretty much f**k all about the right and wrong mods for TFSI engines before I bought my GTI and joined this site, although I did have a fundamental understanding of the principles of tuning and maintenance having been into cars for yonks, just like you. Since I joined, I researched things like mad on here, learnt loads, asked questions, learnt even more, identified the bods that really knew their stuff and really valued their comments, but most importantly I will always stand up and pay attention to the consensus on here. It's what the forum is for. It's a collection of knowledge, with the extra value of (mostly) impartial discussion on top. It's not sales talk. It's not two blokes down the pub. Take from that what you will.