Mike's (rc-monster) motor mount's fit in existing holes and are better because you are not married to the motor. Also the diff mount and motor mount are one so it takes away any flex problems.
I love Mike's mounts. I've got two of them at the moment. My only reason for looking at other motor mounting options is to be able to use mechanical brakes. That is just about the only drawback to mounting the motor on the diff mount. It would be nice to be able to still have the tunability of front/rear brakes. There are always pros and cons. In this case I'm wrestling with the issues of running a chassis mounted motor combined with putting the pinion further away from the motor. This seems to be what Fine Designs does with all their conversions and apparently it works to some degree. I don't have first hand experience with any FD stuff but I imagine their use of modded hardened clutchbells for pinions helps with any mesh issues due to chassis flex.
Mega's own site is easier to navigate than the Mega usa dealer site
click Here then on the picture of what you want to have a gander at, specs are on the same page as the motors.
Hot Bodies Lightning 2 Pro carbon, Mega 22/30/2, MMM, 4s3-5Ah.
Tamiya F201 carbon, Mamba 7700, MM, 2s A123 2.3ah.
Xray XT8, 1518, MMM, 4s5Ah.
Lots of boats. fastelectrics.net