Exhaust?

My Lt's should be here today or friday...so I'm planning my setup for spring time. I'm goin with magnaflows for sure, duals off the headers, into and x-pipe and then the mufflers...probably going over the axle and dumping. I know the collectors are 3", but I've been reading where 3" pipe is overkill on engines less than 400 hp. Should I do 3" all the way back for the sound or will I be a lot better off with 2.5"? Lookin for opinions/advice!

A while back a test was done running dual 2.25" pipes to one merged 3" pipe and this showed to output more power from the engine than true dual 3" pipes. It has to do with engine exhaust gas scavenging and velocity. I didn't pay any attention to it though, I have two 3" pipes with a 2in/2out magnaflow on my truck with LT headers on my truck with the 408 and nitrous setup.