Thanks for the nice comments Tex and John (Neuro)!
I rented the 500mm II for 10 days (this way I get 2 weekends with it), as I figured I could get in at least 2 Football games, and maybe some Soccer too, plus I have a Surfing tournament this week, but the waves are flat right now, they better pick up soon before this bad-boy has to go back.
I'll be deciding between this lens and the 400mm f/2.8II.
I was very impressed with the 500mm II. It feels relatively light for a super-telephoto and it's really well balanced too. I shot with it on a Gizto 5 series monopod, which essentially rendered it weightless. The AF is fast and the lens appears sharp. I shot this game from 11am to 2pm and there was no sun flare and the contrast was very nice too for a mid afternoon game. There is quite a bit more vignetting in the corners on the FF body, than I had anticipated, but I think it looks pretty good for sports shots and in some instances I just corrected for it in post. I think I'll try the peripheral illumination setting. I never had a need for it before. I hadn't noticed any CA either.
I also tried out the new IS Mode 3 and it works as advertised. It didn't fight my movements like Mode 2 does, and I was basically unaware that it was in use. Mode 3 is only activated with the shutter-press and is inactive and in standby while shooting.
Tomorrow I'm going to try and shoot some BIF handheld with this combo. I already purchased the 1.4X III figuring I would need that no matter which super-telephoto II lens I get, since I only had the version II extender.