are there any plans for an HV3 or to mod beyond the downpipe ever? If so, get the 3" IMO.......if you stop with the DP and aren't going to touch it, toss up...depends on preference as the 2.5 is barely bigger than stock, and pretty much just deletes the u bend. Kind of a waste IMO. If you want a deeper tone, or to flow better on higher rpms's get the 3" IMO...