the problem is as an F/O on a PM sector, you would never reject at 80kts because the first incapacitation call of 80?.........followed by 90?........ then think oh dear and decide to 'Reject' as we now say... you are going to be up around the 100-110kt mark anyway at that stage and fast approaching the V1 in most cases.....
plus theres RTO above 84kts i think which is always a good help at bringing things to a halt as well....
My main point was that I try to be sensible and practical about it, and weigh up all the pro'/cons on the day, most of the time debating it with the skipper either on turn around or in the briefing...
I dont think it should be set in stone as it often is with some people..