My situation is a little different than most, so my perspective may not be entirely applicable to your usage scenarios. I routinely shoot concerts in the EV 5-7 range with a 1D MKIII and find myself at 3200 to maintain shutter speed around 25% of the time (with f1.4/2 lenses). Simply put, I am not satisfied 1D MKIII IQ at that ISO under concert lighting conditions - (1600 is good, but there is a significant degradation of IQ, detail, and saturation when you go to 3200). With respect to this genre Nikon owns the space at this point in time... the 1D MKIV and 5DII IQ are not competitive with the D3s at ISOs above 1600, particularly when the light/shooting conditions are less than ideal.
The 5DII does have decent 3200, but lacks the build quality, AF precision, and number of AF points of the 1D; and I have little confidence in its ability to survive a material cocktail/beer encounter (the 1D has taken direct hits from super-soakers loaded with champagne, beer spills, been knocked out of my hand onto concrete floors, etc. - takes a licking and keeps on ticking).
Would say that 80%+ of the shooters I see in the pits are using D700/D3/D3s with 2.8 zooms. Nikon's superiority re: high-ISO (3200+) at this point in time is indisputable and the D3s is far more suited to concert photography than any Canon product at this point in time. Net-Net, like many others am considering a switch to the D3s despite my investment in Canon glass.
P.S. Beautiful grey ghost.