If it came with the XL-5, you got the good slipper. The alumnium idler gear is a good idea, but i never liked the idea of steel and alumnium together and the potential damage to the diff gear, so i'm working on a traxxas SRT that i'm setting up with the new slipper and a delrin top gear as well as the alumnium idler. I think it will be a better deal than steel and alumnium together.

Edit: The RPM knuckles and rear hubs are a nessessary investment as i went through 5x8mm bearings like nothing with a brushed motor, brushless will rip them apart. I would suggest getting them first, because wether you go brushless sooner or later, you'll need them sooner, Trust me, i know

Ordered a Mamba Max & CMS 5700.... Installed them and rear bearing carriers, alum idle gear, and got some various pinions to play with....

MUCH MUCH MUCH thanks to you guys for all the advice and suggestions... Incredible speeds and power... Pretty much solved my main issue... posted a review in the product reviews forum. I haven't really played much cause it got to dark out to see it between streetlights! Can't wait til tomorrow!

cool man sounds like fun!!!! now go get us a vid of it pulling wheelies for miles lol