Wow, I am getting answers from both ends of the spectrum, complete opposite. Very interesting and slightly confusing. I will have to do some research and figure it out...keep the knowledge coming....
I think the reason you are getting conflicting answers is the mild combo you have.
If you needed exhaust from the headers back I would tell you 2 1/2" too. It opens up more options in the future.
For what you have (mild 340) and seeing that you already have a 2 1/4 system, running what you have is win/win. You are out less cash and aren't losing much if anything in performance.
