Thanks for the advice. I've dropped a note to BHP Photo, asking if the 9.25" Kodak aerial film is truly available, and asking what the lead time is on it. Will let you all know what I hear.
Regarding the #8 - I worry that cutting down 9.25" film to 8" would be quite a hassle... and that I'll have enough variables to try to get under my control with a new-to-me Cirkut, that I'm probably better off holding out for a #10 - assuming that a film source does in fact exist. Crossing my fingers....
If film availablility wasn't an issue, I'd go for a #8 for lower price, and easier-to-work-with smaller negs.