Great shots Ian,
I would say it's a resounding YES for the use of ISO 6400, i can hardley tell the difference (publishing wise) from the lower ISO's. Godda give ice hockey a go!.
Are these from the press area or just "track side" seats? are they shot through/over perspex or through the peep holes?. I shoot D2h's so no way could i live with these high ISO's:shake:, Maybe when my D3 (if my wife lets me!:shrug arrives I'll see you there!!. Kind regards Graham.
Interesting to see what you can get with 6400ASA but it's a little difficult to judge the noise levels etc at such small sizes. How do they compare with 1600ASA when you're looking at larger crops?
Having said that, as someone who started out pushing Tri-X and HP5 films to 800/1600ASA to get usable images, who looks at grain/noise if the image is a strong, sharp, one?