I've been practicing with a colleague whose training is as a boxer. He's about 6'3" and weighs 235lbs. His outstretched arm is about 4 inches longer than mine. I'm about 160lbs and 5'8"...
So far we've done 2 minute rounds at speed with light contact to the torso and no contact (but honesty) to the head. We've also gone slower for longer periods and have tried 3 minute rounds.
We play mostly on boxing terms, i.e. I don't kick.
Barring 'cheating' and kicking from far away, I'm getting creamed (happily). I can't seem to get around his jab or return anything. I spend all my time keeping his fist away from me and dancing away from the opposite hand as it comes in. I closed once or twice and discovered the hard way that a short hook to the torso from a large trained man is very hard to absorb spontaneously.
Things that have worked for me are using CMA ideas (and RMAX) to ride, roll around, nodal-rotate around his jab/hook once I've made contact. While I have managed to make contact with his torso a few times by doing this, I usually eat his opposite fist as I follow the jab back in.
I cannot seem to disturb his balance sufficiently to try CMA takedowns or joint-locks. I felt that I had absolutely no power in my punches due to his mass and shock absorption ability, but he seemed to feel I hit pretty hard for a guy of 160. Perhaps he was being nice. I also am thankful for my CMA forearm conditioning - my right arm was fine after our sessions, while his left jabbing arm has been very bruised.
From this brief description, could any of you more experienced fighters/players out there suggest how I proceed - I really like this practice and my partner is a great guy, so I think this will be a long term project.