In regards to power and sound when relating to exhaust...
Mufflers - Generally, the quieter the muffler the more restrictive to flow. I'm sure there are some mufflers that are very well designed and have a better flow at a similar decibel level to other quite mufflers, but in general the quieter the more restrictive.
Exhaust pipe size - A smaller pipe will have less flow than a larger pipe (obviously) but it will also have a higher velocity.
Just like how to large of an intake port can have a stalling effect on incoming air, too large of an exhaust can have a similar effect.
Larger pipes doesn't necessarily mean more power, but neither does smaller.
A larger pipe will not become a restriction until very high rpms or very extreme engine modifications.
However, if the pipe is too large you can lose some of the scavenging effects of high velocity exhaust flow at low rpms, meaning the spent exhaust fumes can stall and revert back into the chamber during the intake stroke.
The trick is to have the correct size of exhaust pipe, one that is not restrictive at high rpms but doesn't cause port reversion at low rpms.
End result? Without dyno testing individual exhaust pipe sizes on your engine combination, you really can't say for sure what a 1/4 or 1/2" larger pipe would do to your powerband. Maybe 1/4 will feel great but 1/2 will kill your low RPM torque. If you have a generally unmodified engine, I'd stick with the original size. It was usually engineered that size for a reason. If you have modifications, it's just a guessing game (unless you have a dyno and some time/money) on what size pipe and muffler to use.
