the best exhaust is no exhaust man anyways
1. not unless you red line it everytime and passes 95 db or something like that
2. i have no idea why it would be bad
3. again you get a exhaust for less backpressure so how is it bad for the valves...

ive ran no catback for a while before i got my skunk2 in and some of my other friends have ran no catback for a while before getting an exhaust and hasnt caused any problems.