I would just get the 3.3. IMHO, the 2.5 should have never been put on any MT.
Even for me on my revo, the 3.3 is a bit weak, but it gets the job done far better than the 2.5R did. I'm used to running a true big block on my revo though, so "weak" is a relative term. Before I ran a big block, the OS18TM was what I had and it did ok, about on par with the 3.3.