I was running an FMF. So, yeah, HUGE improvement. I was never around a V1 pipe so I don't know how they were. My Zilla has HRD porting from 500 Fanatic so the new pipe really works well. I could lug it around and it would always come right back on the pipe.
Here are some pics of my rebuild.
https://picasaweb.google.com/112870329437558822203/500