70-200 2.8 is a nice all round lens - tend to have that on 80% of the time
Yes - any lens at 2.8 is good for this.
They used to do a 1.8 lens at 200mm (I think) - that was a nice focal length - but sadly they stopped it a few years ago.
The new 1D MKIII goes up to 6400ISO!! So it should be even better in these situations.
The existing model will write to both at the same time already - but the new MKIII will write to one card and then continue automatically to the other card - which is good
Nothing on the 40D yet though
at the moment - but expanding all the time....) 
