The only trip that bothered me was one year we stayed in Gunnison (7,700') overnight and then horse packed in and camp was at 10,700'. I had the worst headache of my life. Rest, tons of water, and food had me feeling fine 24 hours later.
Most other times we camp around 8,500-9,000 and hunt up to 11,000+...I've never had a problem doing this. I did take Diamox on another trip as a preventative, but can't really say whether it did anything or not.
This year we plan to go in and camp around 10,000'. I'll be taking Diamox again...can't hurt.
My experience fwiw...I think it has to do a lot with recovery altitude when sleeping...if you are sleeping above 10,000 it is so much harder to recover from the days exertion. Your breathing speeds up to get more oxygen, and in turn you expel so much more water because of the increased breathing rate...dehydration can sneak up on you and that leads to most of the problems.
The rule I always heard is that it takes 1 day to acclimate for every 1,000' when you go above 8,000. So 2 days to get acclimated at 10,000, etc.