3" over axle is entirely possible with no clearance issues, it just takes a bit more time and hence $ if you can't do it yourself. I built one for my 242. By built I mean I took a 3" exhaust off a car I had and ended up pretty much redoing the whole thing because it hung to low and at full suspension compression interfered with the torque rod bracket on the axle.
Back to the question at hand, 3" future proofs your build. Your not going to save much $ by only going a 2.5" which might not meet your future needs.