Hi Vincent! I'm a bit of an Iridium flare freak and have always found the info given on Heavens Above to be spot-on in time & magnitude. EXCEPT for one embarrassing episode at Snake Valley, Vic, where a promised mag -8 flare failed to eventuate.
But I think that was 'pilot error' - ie I must have mucked up the location or something.
Re astroron's comment about mag -8 flares being close to overhead, I don't think that's quite right. They can be pretty much anywhere.
Cheers -