Pipes make more power, but they as with most any modification can reduce reliability. If I were to pipe a sled, I would use pipes that go into the stock silencer or one that is comparable and quieter. Like glasspacks on a car or truck, they will be louder and as the fiberglass breaks down, louder yet. SLP and Aaen make good products and are comparable in power and tuning. When I had Aaens on my 91 Indy 650 and the 95 XCR 600 I ran with and against guys with SLP set-ups and we ran side-by-side. SLP and Aaen are the most trail friendly in terms of torque and useable HP IMO. I know that SLP made pipes that go into a common silencer. Not sure if Aaen did. I had Aaens on my 95 XCR 600 and they made good power and were fairly easy to tune, but any time you run 1 pipe for each cylinder, the motors require constant jetting for temps otherwise the sled may perform worse than a stocker. A Tempa-Flow is a good way to keep from having to change jets all the time. It is also important to keep the pipes hot as they are more efficient.