I find that even 3200 is usable from the 1D3 with some NR from topaz denoise
generally i try and keep to 1600 but will bump it up if needed
Another APS-H user! Maybe we really are related
I'm going to keep my eye on the used 1DIV market once the 1Dx is finally released
I love my APS-H especially with the 16-35 II on it even wide open its lovely and sharp and gives about 20-48mm effective which is a really nice range for walk around or for receptions events where you dont have alot of room.
and i'm also keeping close tabs on the used 1D4 market