The emaxx2 (3905) is a lot better than the old emaxx in terms of durability.
The drivetrain is very strong and will hold up to a lot of use and abuse.
The gears are module .8 and sad to say you can't put a revo module 1 gear in it. You have to use the spur gear from a monster GT if you still want to go module 1.
I use a 1515/1y/F running on 4S controlled with a MM with the hole mod and dual fans on my 3905. My gearing is 68/22. Our club has a restriction so we're allowed to go 4S as the highest number of cells to use.
I hope this helps a bit.... Happy wrenching!!!