Last night I discovered that my current ballhead slips ever so slightly with the 5D MKII and 100 2.8L IS Macro mounted. The head came with a Manfrotto 055XPROB and because I was shooting mostly landscapes with a 4x5 riding on a 410jr., the ballhead didn't see much use.
Maybe on a subconscious level I've known this but just forgot about it and could be the reason I've been considering a RRS BH-55.
Still need to play around some. Maybe tonight.