I thought that it was much more responsive and the top end was definitely stronger. When you get the factory dump off, have a look at where the wastegate dumps to... it is basically a solid bit of metal about 5mm behind the wastegate. Don't get me wrong, while some people say that it is worse with the dump, simple fluid flow theory tells me that the lesser the restriction, the better.
I think Benm posted a thread with before/after dump and front pipe dyno figures, i think this is a pretty good indication of an increase.
Remember that all i have is a 3" dump / front pipe, a 'race' cat that flares out into a 4" Trust cat back, and a pod filter. I have 174rwkW, which i think is pretty good... Who is doing the exhaust system for you? Nizpro? I'd love to see / hear it when it is done. Below are links to pics of my system.