I bought the middle size one last Christmas but still haven't had a chance to get out in the field with it. I bought it to use with my 4x5 Tachihara and it seems like it should be fine with it. But then, the Tachi only weighs 3.5 lbs. I think it will also be fine with my Bronica SQA with the wide angle lenses I normally shot. I doubt if the middle size will work for you.
You would have to go to the larger size but with the jump in price between the two, I'd look at a Giottos for about the same price. I had looked at them when I was buying and would have like to get one but the cost and the extra 2 lbs were more than I wanted. My middle size Flashpoint with my Bogen ball head comes in at 3 lbs., just what the doctor order for the New Mexico mountains.