In addition to my Nikons, I shoot medium format as well. From your experience, will the M10 adequately support a med. format (Hassy/150mm)or should I consider the M20? I'm trying to keep the weight minimized. Though the Markins web site is out of date, Mr. Mah has patiently provided me with product info. and current prices. User input really appreciated.
I don't shoot with a med.format, but I have shot with my 300mm f2.8 and f-100 on my m10 ballhead. This load should more than equal your camera set-up. I think it's more of a leg limit problem than a head load. With the quality of a Markins head, I feel that soft photos will be caused by the tripod legs and not the head. Hope this answers your question.
I am a little late to this party, but will offer one brief comment. I had to make the same choice, M10 vs. M20. I shoot an F100. My largest lens is a 300mm AFS (weighs about 5.7 lb.). I consulted Mr. Mah by email. He recommended the M20, and I followed his advice. However, from all I have heard about the M10, I think it would probably be sufficient. The point is that Mr. Mah, being a very helpful gentleman, is available to help you with your decision. Notwithstanding our distances and time differences, his replies to my questions were always timely, polite, and helpful. We are fortunate to have him as a member.