2.5 or 3.0 exhaust

I purchased a 2.5 in universal X Pipe kit and a set of Dynomax 2.5 in
Ultraflo welded mufflers about a month ago.A couple of my car buddies
think i should use a 3 in system. I would like your opinion on this. The
car is a 72 Pro Street Demon. Motor is a .030 over 340, 11-1 Trw pistons,
Cam Dynamics solid lifter cam .585 lift, duration @ .050 is 260, Hooker
super comp headers 1.75 in diameter, 750 Holley with Proform main body,
4:56 gears with a 29 in tall tire. Heads are ported X and a Victor Jr intake.
Motor spins to 7000 rpm .Thanks for your input.