Please understand that I've only been doing the 1/8 scale thing for a few months now, but have built five conversions and have done a lot of experimenting. Thank goodness for inexpensive motors like the Feigaos which allow for all of that experimenting.

I've found that with larger vehicles, like trucks and even 1/8 scale buggies, rpms are something that you want to avoid. Keeping rpms relatively low, keeps the motor in its best efficiency range thereby avoiding unwanted heat. You can usually make up for the lower rpms by running more gear to get to the speed that you want. Once you find the proper setup for your vehicle and power source, you'll have lots of trouble free running ahead of you.

Right now, I'm running an 8XL on 5S lipo in my Muggy (which is a big heavy truck) and it's fast enough to be considered stupid for a monster truck and the torque is unbelieveable. I took mine to a party thrown by the owner of my LHS this past weekend. He's been in and around RC for over 20 years and when he saw my Muggy run, he said that he'd never seen anything like it before in his life. He gave me a Losi 8ight T to convert for him.

If you go with the 10T motor, I think that you might be a bit disappointed with the top speed, although the torque is going to be rediculous. I think that in a heavy maxx, a 9T would be a good solid conservative motor with pretty good top speed and more than enough torque to sling shot you out of holes. If you go with the 8T, it'll get pretty stupid. I've ordered a 9XL for my truck. The 8XL is plenty of fun, but just going fast isn't as much fun as it was when I first put it together.