Which one do you think is more bang for the buck? I am also asking because I cannot find any good reviews for either.
there both a bang for your buck u cant go wrong with either personally i think the 4xl shape is just to bland and round i love the oscillatrix shape
I know the werrd is stackable, but is the oscillatrix?
Without serious mods, no. It would probably make it vibey anyway. I say 4xL. 
4xl all the way.