They all have the same hp.
The RS only comes in white and red and is lighter than the others.
It also doesnt come with a spoiler.
The MR is like a regular EVO but comes with a 6 speed instead of a 5 speed.
It also has a few other little things.

Go to mitsu web site and look at the three.
I like the RS alot but I want a black one like my galant.
So I will end up getting a regular evo in black with no sunroof and just take the spoiler off.