It's been a long time since I've used the 300/f2.8 AF, but I don't remember it being particularly sluggish on an F5 - the D3 is not slower than the F5, although I doubt it's much faster either. (Not in this department, anyway.)
I've only used the 120-300/f2.8 on D3 and D2x cameras, so my experience is not entirely comparable. My impression is that the 120-300 is a bit quicker focusing than the screwdriver 300/f2.8, and certainly not as fast as the more recent 300/f2.8 AFS VR-I (or, presumably, VR-II). Still, I see this one used regularly for motorsports, and I borrowed one once to shoot dog trials and baseball - I never thought about focus speed. Ever.
I don't shoot hockey, but I don't imagine that it would be too much different than baseball, in that you have relatively known or predictable focus targets, followed by a 100+mph "warp" to another, somewhat less predictable focus target. I'd guess that either of these lenses will do the job on a D3 or other top pro camera (CAM2000 or CAM3500). If anything, I would think that hockey is a little easier as the backgrounds are often the white ice, so the AF systems have an easier time getting contrast, and that would tend to minimize the effect of an AF hunt.
If it were me, I'd probably go for the zoom - it's a LOT more flexible.
_____ Brian... a bicoastal Nikonian and Team Member
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