I too went from 40D to 1D for sports and I wanted the IIn but then realized I could keep my Tokina 11-16 to go with my XSi if I got the cheaper Mark II instead. Boy am I glad. The Tokina 11-16 is a fabulous UWA on the 1D!
Comparing the 40D to the 1D II here's what I see.
- AF is much, much better.
- Viewfinder is nicer (sharper, bigger)
- Weight is significantly higher
- No more bolt-on grip that is never tight
- Using the LCD to review images is almost useless
- Flash exposure is off by about 1 stop by FEC corrects it just fine.
- IQ went up
- High ISO noise is about the same
About the LCD - The 1D II has such a small / poor display that it is pretty much useless for confirming focus or stop action. I can use it to review the histogram but only if I'm not outside in bright light (overcast or brighter). So, I've quit looking at the LCD and I just shoot.
Actually, the bulk of the user interface is not as nice as the 40D. You always have to hold one button while pressing another to make the camera do anything. This means changing ISO or WB, viewing images or histograms, etc. takes 2 hands. Hassle. But it also means you won't accidently change mode, ISO, WB etc.
IQ is higher with the 1D too. Colors are a bit richer, things are a bit smoother, all my lenses are a bit sharper.
Battery life is somewhere around 1000 frames - very nice!
My 1D has 70K clicks and I paid about $1100 for it. It has some minor exterior "battle scars" that I didn't even notice for the first month. I'd love to upgrade to the IIn but there are better things I could do with the $500 it would cost.