i have been running an S9550 in my 4wd for a couple of years now, initially i bought one to go in my X10, as it allowed me to get the esc in behind it, and then I swapped to a ZX5 and put it in that....
to cut a long story short, the S9550 has never let me down, and I drive the lazer a lot more aggressively than I ever drove the X10
