More weight = less power regardless of the machine.
BUT!!
I have seen a 400EX go through an 18" deep mud pit, with 2 male riders on it, one weighing 230lbs, the other about 170lbs, and they made it through, JUST barely, but they made it.
Needless to say I was pretty impressed.
Hanging with a Raptor will depend on your skill level as a rider more than your mods, but there are quite a few upgrade options for the EX to add some grunt.