I'm on the fence with exhaust but I'd be more keen (yes, keen) on the 2.5 as 2.25 just isn't that much of an increase but $$$ For now, I've been enjoying a very quiet ride!
I had a quasi 3" exhaust for my Mazdaspeed6 when I first bought it used. It was loud but it did have a very nice low note and actually helped spool up compared to stock mufflers with a 3" downpipe.
2012 SGM Ti DCT Stock and loving it
OEM multispoke 17" with stock rubber summer-X-ice 3's on stuck rims = awesomesauce