Here's my personal experience and maybe I'm a genetic anomaly.

My max HR is 192 - I've seen it a few times on HRM monitor and when I was tested that's about what they projected.

But I can ride for hours in the 160 - 175 range. My average HR on Saturday for the first 86 miles was 164. I don't know what it was after that because my monitor refused to go above 120.

164 is about 85% of my max. My personal experience says that you can train yourself to sustain a higher heart rate. When I climb Diablo, I'm usually up above 175 for a good chunk of the 10 mile climb. That's about 91% of my max.

Like I said, this is all anecdotal and I may be odd. Well, I know I'm odd, but you know what I mean.

V.