Thanks Greg - you're quite right. I really would loved the 5D Mark II with a faster lens. I had to use my 17-70 rather than the usual 24-105, simply for the wider field of the 17mm, but also because the 17-70 is f/2.8 and the 24-105 is f/4.0 - too slow for astro shots like this (or timelapses).
There's been some great shots where it's a single shot of 30-60 seconds, but most of those were when the comet was brighter and had some nice foreground.
Most of the great comet-only shots were tracked and didn't bother with silly things like a foreground
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I think you could track the comet and also get a stable foreground.
It would mean you would take an LRGB series or in the case of a DSLR a few shots of the foreground with the tracking turned off and then use a layer mask to insert it into the final image. I was considering doing that with one of my shots not yet published with a tree in it. But when time is pressed between 3am and 4:30am some things have to be put aside to get a decent image at all. If there were more time or you planned only the one image that'd be the way.
Greg.