Gearing Suggestions? E-Revo Brushless Edition

I have an E-Revo Brushless Edition on pre-order, and it comes stock with the Castle MMM 2200kv combo. The stock gearing direct from Traxxas is 65/18. I am looking to order a couple other variations for the spur and pinion just to have on in hand....just in case. Let's say two of each. Please understand, I am not an "RC Newb", just a "Brushless Newb". Any suggestions? Thanks! And this isn't a "What am best gears?" thread either as Neil might refer to it as!