I'm still trying to decide which MF system to bankrupt myself with but having handheld the H3D with 50-110 zoom for over two hours I was surprised that it felt, if anything, more comfortable/less painful then my 1Ds2 with 70-200 zoom. (I'm only average build - about 5' 10 at the start of the day down to 5' 9 by the end!) The balance felt better on the H3D - maybe the grip helped. The Canon/70-200 definitely feels like it is pulling forward. The Canon clearly has the edge for "pointability" though, as you'd expect.
I just came back from a 2 weeks vocation in Tibet not long ago, with Leica M8 and H3D39 with some lenses, include HC 50-110 and HC 300/4.5, I can tell you H3D39 with 50-110 attached to carry for 2 hours will be very tough for me. Apart from the ergonomic issue, the Lowepro AW back pack I have can put a Conax 645 body+P45, 4 extra P45 battery, 35mm, 55mm, 45-90mm, 120 makro, 210mm and 350/4 but can only out a H3D39, 28mm, 35mm, 50-110mm, 120mm and 80mm and 2 spare batteries. The system accessory is also an issue. With H3D system, you will end up needing 67mm, 77mm, 95mm filters and with Contax it is only 72mm and 95mm. My finding on H3D is that the grip feels good when you are shooting, but you need to try when you are not shooting and carry the camera around just holding the grip.
I shoot a lot of fashion in location, many times need to use a bron-color ring flash attached to the camera, with the ring flash and powerpack considered, and the camera and lenses, I must say Hy6 is extremely tempting for its size and weight and the possibility of custom of holding the camera in one orientation and just rotate the back.