[cycleguy55]

Points to consider:
- 2.5" I.D. will be quieter than 3"
- Longer will be quieter than shorter
- Louvers facing forward will be quieter than louvers facing rear

You already know your mufflers will be a bit longer than most, so that will mitigate the sound level a bit. 2.5" I.D. is probably big enough for your engine, as you've noted.

It seems to me the question becomes one of which do you prefer: a) a quieter rumble; or b) a slightly louder exhaust with a bit of attitude?

Sounds like a real dilemma to me...