Well first off, what do you plan on doing with it? I think your LHS may be leading you astray before you even get going, mainly because they have "old" revo's they can't get rid of. The altitude only effects tune not so much your performance. I find their statement to be really off base as the 3.3 which is a .20 (midblock) is considerably faster than the 2.5 which is a .15. The 3.3 is about as quick as an OS .18TM which many 2.5 owners end up putting into their Revo's (me included when I had one). If you plan to or think you might race at some point, go with the 3.3, the longer wheelbase alone is a big help on the overall handling of the Revo which is already a great racer. If you plan to just bash, then you can get by with an older model, tell em to make you a better deal cause they need to get rid of their older merchandise! LOL