Might want to check out the Hitec 645MG. Run about $30-40 and is a great drop in replacement for the stock traxxas servo. I run these in 4x4 slash's and my stampede and its alot faster than the stock traxxas servos.
if needed you can step up to the hitec 985 or the 7955 which I use in my 1/8 bl conversions.