Ok the about 300mm, actually it looks like this will be in the year to come and by then I would probably look at the 100-400, so I can always get another ballhead.
My setup will be the 5D,grip,70-200 F4 IS, 1.4 TC.
I was thinking of going with the Manfrotto 055XPRO tripod and the head in question.
I will look into the 468 as another user said that the RC2 looks rather weak and should go with a A-S type plate.
I think the Manfrotto range are at the lower end of acceptable heads, at least based on my own 486RC2 experience. They lock down perfectly well, so no need to worry about that, but do "droop" as you lock down and theres no "sweet spot" like you get with the Markins range.
The latest Manfrotto line up might be better, so feel free to ignore me thus far. However I'd suggest that even if you choose the 488, go for an Arca-Swiss style quick release system. I always worried that the RC2 system would dump my expensive kit onto the floor. It never did, but it was always on my mind.