A fairly standard rule is a mild 4 cylinder system is done with 2.25", as any larger and you can actually decrease performance due to lower exhaust velocity and too little back pressure. There is a whole science behind it, but unless you are really, really experienced in tuning, and have the equipment to test-as-you-go I suggest sticking to the conventions, and not straying. Sure it's 'only' another quarter of an inch, but that is actually an increase of 23% in area and you won't have the flow to support it.
Going from 2" to 2.25" is an increase of 26%... that's a huge jump to begin with. Going to 2.5" is a 56% increase over stock... Wow.