Welcome Ron!
Honestly, i have been mauling over the same question in my head for when I do get my 3905, my difference is that I'm running 4s lipo instead of Nimh.
As of now I have 2 MMM esc's, a Medusa 36-70-1600 motor, and a Tekin 1700kv truggy motor. I'm thinking that one of these motor's will end up in my Emaxx on 4s with a taller gearing. Should lead to longer runtimes and cooler temps. I then have the ability to throw 5s or 6s in there if desired.
But I have also been looking into the MMM/2650kv combo. This is a plenty powerful setup. I actually ran this in my 2.5 Revo conversion before I moved it into my 1/8th buggy. The 2650 is a super strong little motor and should have no problem moving the Emaxx around at 40mph or higher if desired.
I have been toying with the idea of running this motor on my 3905 for a while.
Good thing is, you can pick up a refurbished combo from
http://www.castlecreations.com/produ...r_refurbs.html for $225. You can't beat the power for money there.
But being that you are using NiMh's still, I would suggest gearing it easy for around 35mph, otherwise, you may start killing those NiMh packs. I would start off around 16/62 gearing or maybe a 17t pinion also.
then once you go lipo's you'll be able to gear higher for more speeds.