Al
I think the camera response curves are going to be dodgy for a few reasons. I'm not sure how we can avoid this. The A stars (like sirius) arn't very bright in the IR so the levels are low compared to the green etc. When you try to divide another spectrum by this curve it enhances the IR more than it should. I tried this with a red star and got a vastly enhanced IR end to the spectrum that wasn't real.
The same problem will occur if you use a red M star as the response curve and try to calibrate a hotter star but with the opposite effect of over enhancing the blue end.
I suppose a more realistic result would be achieved by making a curve from a "B G and M' star and averaging them. The difficulty here would be how to normalise them first so that the weighting for each spectrum was even. Maybe normalise all of them at a specific green frequency and go from there.
In the end I don't think it matters terribly as we arn't measuring the flux at a particular frequency although this is possible with reference stars etc.