I used to wanna be skaarj...
I tried changing to the skaarj just for the dodge anim, but I couldn't stand being the marine on servers that didn't have the pack. I never noticed my game was any better from the weird dodge anim though, and I dodge like a fiend.
I admit, the cow model was weird at first, but I rarely aim for the head with the weapons I primarily use, and now that I know where the head is, I don't have a prob anymore.
It doesn't seem to make a difference. The only people I lose too are ususally using basic models, like male or female commando, and nine times out of ten I swear the belt is a part of their model. Serious dependency problems.