Never heard of a gimbal head being used for video - how smooth a motion can you get without fluid opposition to your hand moving? Especially with a long lens, is assume not very.
Get a decent fluid head imo, unless anyone can advise otherwise :s
I usually use the manfrotto 504 heads, but at focus I was VERY impressed by the new unreleased 502 head - miles better than the crap 501, and apparently its only going to be about 30 quid more. Depends how much weight you're gonna put on it