"True" 7.1 processing is limited to Lexicon's Logic7 and Dolby's Pro Logic IIx. Dolby Digital EX, DTS ES, and Cirrus Extra Surround (the three processing modes that the 950 offers that generate surround back data) produce a mono signal sent to one or two surround back speakers. Dolby EX and DTS ES encoding is available on some movies, but the processing can be applied to any 5.1 movie. Additionally, the 950's CES processing can be used with any 5.1 mode (Dolby Digital, DTS, or Pro Logic II), so you can use the surround back speakers any time you are using a surround mode. Personally, I've enjoyed having the surround back speakers, and in a room arranged so that 7.1 can be made to work I think it's a worthwhile step to take. Of course, it means adding two more speakers (and in some cases stands or mounting brackets) to your shopping list as well.

With your existing Paradigms, the extra 100W of power would probably rarely or never come into play, even during those action scenes. Since the other channels will have even less need for the extra power headroom, you could consider getting the 7100 now and later, if you want more power for the Monitor11's, you could add a pair of M200's for them - that's what is driving my Paradigm Studio/60's (which are about 3dB less efficient than your Monitors) now, and it's a great combination.