The maximum ISO setting of the camera is not in the manual, I just checked it on the camera using the ISO control. So the flash is the limitation with respect to the highest ISO you can use.
I just looked at my AF280T. The highest ISO setting on it is 800. But I don't think that changes anything electrically. It just shows you your ranges at each f stop. I may burn a test roll and try it at ISO 1600 and see if TTL flash is accurate.
Pentax's 645, ME Super, Spotmatic II
Minoltas SRT 102, SRT 202, Maxxums 7000 and 7000i
Canons A1(X2), EF, TX, FT QL, EOS 630
many Nikons-black F2 eye level, chrome F2AS N90s, F4E, N2000, N6000, N6006, Nikomat FTN, N5005