Exhaust questions

[coyfish]

If I buy a 3 inch testpipe but a 2.5 catback will there be problems putting it together?? Also what are the pro's / con's of 2.5 vs 3 inch exhausts. Obviosly 3 is better (for power) but there must be benifits for the 2.5 . . . Does the 3 rub a lot more or something? Also can someone explain catback vs dual catback for me. Catbacks are about 350 bucks cheaper(then the dual catback) and from what I understand you only get well . . . 1 exhaust instead of the dual tips like the stock. Ive seen a million videos of "catback exhausts" on speed 6's but they all have dual tips functioning out the back.
Any help would be greatly appreciated

[wannabe]

as long as the flanges are the same its not a problem.

as far as 3 vs 2.5, the main reasons for smaller are lower cost, more back-pressure (debatable if its *better* though).

typically, cat-back is a single exit exhaust, dual cat-back is the double exit, like stock.