Pipes are kind of a personal preference. Personally, i am a white brothers guy(even thought they just recently ceased production). I think that they sound the best. But everybody is looking for something different in their pipe. The Powerecore 4 would be a great choice as well. I have a friend who has a z400 (basically the same quad as yours) and has a powercore 4 on it. It sound good and it gave him better throttle response and power. I would say the best thing to do would be to do a little research, read some reviews and find out what you are looking for in a pipe.
B.T.W. Lots of places still have white brothers and they are on clearance right now just check out dennis kirk.