I use the Bogen/Manfrotto 055 Nat (metal, not fiber) and their 393 gimbal with my Canon 500mm f/4 IS. I cannot complain for the money. Fully extended, the tripod is a little shakey with the prime on it, but I don't use it that way in any event. I'm virtually always sitting on my little Walkstool, and extend only the middle segments (not the 3rd segments) and spread them out to the first snap wider/lower than the standard position. This puts it just the right height for sitting comfortably, and is quite stable when used this way.
I must admit the Wimberly, Jobu, etc. gimbel arms look more elegant than the 393, but unless you can justify the expense, they are simply outrageously expensive. Same holds true for the Gitzo tripods. Two of my friends have gitzo fiber legs and both of them are broken/cracked. Not necessarily the fault of the manufacturing, but it makes me leery of spending that kind of money for fiber legs if they seem so easily broken. Perhaps some day I will luck onto a steal of a deal for such kit when somebody wants to upgrade theirs, but I can quite well make do with what I have and glad to have it.
By the way, if you do get the 393 gimbel, take the rubber knob off and put some clear silicon under it, then put it back on. It'll keep it from accidently coming off the metal tension knob that it covers.