Originally Posted by CraigMBA

Depends on the track you are running on, and how much power everyone else is.

I ran a 6.5 and a 5.5 540. The handling was great (much better than with the 4.5 550), but if you needed the snap off the corner to jump the "send it" triple they put right after the hairpin...

Lets just say you can't jump it and everyone else can. Expect to get run over - often. And you'll ABSOLUTELY need a fan. Ultimately, I bought a four pole.

The Hobbywing 4 pole is really nice. It has a nice power band, is about 3 ounces lighter than a 550, and has better torque. I'm a big fan.