It should help it positively. Even moreso if you put a PC III on. The stock pipes have a shit load of chambers in the baffel. When you put an aftermarket pipe on its a straight through tube making less negative backpressure. You should be set.
Slip-on exhaust alone wont gain you any power, and wont loose any power..Its all for looks and sound
But i noticed now that i removed the ex-up with my new slip on (see signature pic) I do get a slight bog now when i take off from red lights..Nothing bad enough to even care about really, its very minor
The power is all gained when you put on a mid pipe, or full system + PCIII