Stacking REL Subs

Looking for feedback from anyone that has tried stacking the REL G2 or G1 subs? Was it worth the cost and effort?  Two G2's are pretty powerful and make a very noticeable difference (improvement).  Using two works great with Magnepans for sure.  Wondering if stacking and using two per side would be even better?  My room is fairly large at 22 w x 29 L with 11 ceiling.