When I first got Pentax autofocus (SF1n) I got a Lowe Pro Magnum bag. I bought a used one for my Hasselblad mostly as the zipper was not working good on the original bag and a used bag was cheaper than repairing. My system has a 500 C/M, extention tubes, lightmeter, a prism and waist level finder, 2 to 3 backs and perhaps 4 lenses (2 are mine and 2 are semi-permamently borrowed). Also room for filters and film of course. The waist belt helps with the load but if I was to carry it any distance I would use either the sling bag I have for my Pentaxs or for more room but less suspension I would use a Lowe Pro Omni Trekker only because I have one for my 4X5. If I was buying new and looking for a shoulder bag I would also look at the Domke F1. My wife has a F2 and has recently obtained a back pack harness for it but has not yet used it.
My Hasselblad outfit not inclucing the 250mm is most likely less weight than the D200, 17-55 and 70-200 outfit I used to use and filled the Domke F2 at my previous job. Need to see if I really want to tote the 250 around much as without it I can get the K-r and two or three lenses in the bag.
Many bags will work depending on your style of shooting and the distance you need to carry it. MF is not much larger or heavier than a pro DSLR. An exception is the Fuji GX680 which fits nicely in a SUV or minivan .