I'd bet my truck that the radar gun he is using is not reading accurately. Supertib clocked an XTM 247 powered Savage at somewhere around 55mph using a radar gun, then switched to different tires, and was getting readings of mid 30's. Truth is, you need a very good quality radar gun to accurately clock Nitro MTs, because cheaper guns will often read the velocity of the top of the tire. That truck is probably close to 50mph.

About the gearing, I'm sorry, but you have no idea how fast 50mph actually is. The difference between 45mph and 50mph is the difference between a stock Savage XL running the low revving 5.9 engine and the terrible HPI polished pipe, and supertib's highly modified Picco 28s running an 086 pipe, similar gearing and identical tires. Using the highest gearing you could fit in your Revo, you would be lucky to break 45mph.