I just sold my C.A.B. M because I'm planning to pick up the Captor X.
The C.A.B. M is great. I used it at a couple of gigs. My use was for running a signal to front of house that I could tweak separate from my amp on stage.
Ultimately, I wanted to have my stage volume to be somewhat independent of what I sent to the FOH. The ability to choose IR's and add effects was really cool too. I found a stock 4x12 cab and sprinkled a little reverb in and I was golden.
I don't "need" the load box... but I figure it can't hurt. If I can push my amp harder at small venue friendly volumes while still getting everything the CAB M gave me... Why the heck not???
Hope that helps a little.
Feel free to PM me if you have any questions.