Z32 AFM and SAFC-II should work.. in theory. Where's steve-sst when we need him?
The difference between cars could be explained by variance in the afm's operating voltage over a (up to) 10 year period. I mean, when the car was new, they had to deal with climates that included seasonal snow, so the afm should really be able to handle cold, dense air without freaking out. That's one possible theory, but it's probably not the right one.