Hiya Shaun, your MM and 6XL should be there next week
It'll be interesting trying to get a Revo to handle 80mm power, I have one in my Muggy and it's insanely powerful. The FoC gear in the transmission is driven by a little pin (2-3mm diameter) and that pin is very prone to shearing under electric power. You've just got to drill that hole out and use a tougher pin and the trans is pretty tough. A piece of hex driver that is the correct diameter should suffice. I wouldn't bother with RR steel gears unless you strip the stock gears. There are a lot of people that do the simple pin upgrade and the stock transmission is pretty tough.
I sent Daniel 1 E-Revo diff, he'll probably want it for himself though

They're supposed to be improved over the regular diffs but make sure they are shimmed. 1/8th diffs will greatly improve the durability. There was someone here who managed to fit Muggy diffs into a Revo with only minor modifications to the bulkhead, I'm wondering if a Cen Matrix Buggy diff would drop in since they use smaller gears. The RC-M hybrid diff is a very good upgrade, but it's also expensive. Keep in mind the 1/8th shafts are all 8mm as opposed to the Revos 5mm (I think it's 5mm, not totally sure though). RC-M has a variety of parts available for toughening up Revos, I'd go with 8mm shafts all around if you can afford it.
That tranny pin, the diffs, and the U-joints are the major weakpoints in the Revo's drivetrain. With that 80mm MedUsa you will snap a U-Joint, it's just a matter of time until it happens. The new shafts coming out with the Summitt and BL-Edition E-Revo should be tougher than the stock units, but you may want to look into some CVDs for it.
EDIT: Stickies rule:
http://www.rc-monster.com/forum/showthread.php?t=7441
EDIT Again: Here's all you need to know about the pin mod:
http://www.rc-monster.com/forum/show...8&postcount=45