Rel storm III or Stadium III.

I'm using Vienna Acoustic Beethoven for the main set up, Maestro for center and Haydn for surr. Currently I am using M&k V125 subwoofer for home theater(30%) and music(70%), I want to replace the subwoofer on my system, should I go for Rel storm III or stadium III? will it be any different between M&K V125 and Rel Storm III? Due to budget limitation I can only get Storm III in a couple months or I will save it up for Stadium III within a year. Any suggestions will be apreciated.