Roland TD4 models (what's the difference?)

Hello,

I'm on the market for a V-drum kit, my budget is about $1000. I'm thinking of going with the Roland TD4, but I notice there are many different models of this (k2/ sx / kx / kx2, etc). What's the difference in the models?

Regards.

Some have all mesh pads some have a mesh snare pad and rubber tom pads, also might be a difference in cymbals set ups as well.