60mm Muffler vs 80mm Muffler, Difference on stock? Options

[Guest_Jason_*]

Obviously the 80mm is for Turbo, and 60mm is for running Stock, I know that.

I'm ditching my current Arospeed Custom Catback Setup to get something different. I'm looking to get the Apexi N1 Muffler thrown on a new Custom Catback Setup but I do not know which size I should get. I'm currently running some simple Mod's under the hood, but everything's bound to change in the next month or so by getting upgraded, like Short Ram to CAI. Anyways, i'm going to be Turbo'ing my ST before Spring but I want to change the Exhaust ASAP so I can get my headers installed right away as well. Think it will kill anything if I run a 80mm Muffler on a Turbo-less engine for a little bit?

Also, do muffler shops install headers? :\