Proud owner of 400 mm of prime glassMost monopods from the high quality manufacturers will cope with a large white. Gitzo tend to be very expensive and their tripods look the part, but I don't think their monopods can command the same superiority, because there are a few decent ones around. I've started steering away form Manfrotto tripods, but their 680B or (681B?) will cope and appears to be better made than their tripods. Also have a look at Giottos, as their tripods are better build quality than Manrotto, so I would expect their monopods to be at teh same level, although I haven't looked at them closely, the Giottos MTL 8261B tripod I have more than copes with my 300 f/2.8 and was much more reasonable than the Gitzo equivalent.
Can anyone suggest a suitably sturdy monopod.. no way anyone can hand hold such a beast and get half decent shots!
I have a Giotto CF tripod which I am very satisfied with, but a 400 mm needs a monopod, or else a gimbal head on a tripod? Although unsure what gimbal to go for, except Wimberley have a good rep with the version II of their head, although have no idea what brackets would be needed for a 400 mm