rly_stupid

i'm sure i'm not the first to ask but...

i have an 06 gt and so far just an intake, slp lm axle-back, 93 oct tune and 4.10 gears.

i'm looking to get the pypes LT and x-pipe with high flow cats. brenspeed has them for 670 something but theyre 1 5/8". i say this because in the future id like to get a novi 2200. now would it be okay to go with that size LTs or do i need to go bigger? if i do would it hurt to have them on while i don't have the SC?

last thing is anyone running this setup w/ or w/o the SC? thank yall!