at 6400 I'm noise free printing to 11x14
and at 12800 am virtually noise free printing to 8x10 (haven't needed to print larger yet)

there are some tricks, which I know the 5DII has, along with my 50D's and probably the other newer Canon's

JPG, JPG, JPG ... RAWs at this high ISO are NOT PRETTY

the cameras have an option under Custom funcition ... High ISO noise reduction ... mine is set to strong

this alone is all I've ever needed to do up to ISO 6400, that and over expose by one stop, and I have amazing prints
now that LR3 has goon NR too, I've began pushing to 12800 because when winter came, the outside ambient dissappeared, and I couldn't even get up to 1/200th in the barns at ISO 6400 anymore LOL

I own two 50D's, rent more when needed, one assistant has the new 7D ... and the image quality is not noticably improved under the above conditions, so I'm buying another 50D until Canon improves upon these two bodies, but for under $1K the 50D is a sports shooter's dream camera LOL