Interestingly, 2 months ago, my Cardiologist did some sort of stress test as he wanted to see how my heart was pumping and so forth. They stopped me on the treadmill when my heart rate went to 141 which "they" said would be 90% of my max heart rate. At that point they laid me on a slab and did some ultrasound on my heart at that level.
Doing a little math, the 220 minus my age (65) is almost spot on. That is 155 and then 91 percent of that is 141 and change. So, in my case it was accurate. Turns out my heart action was fine and everything checked out OK.
Translating that to the bike, I rarely go over 145 and then I use 140 as a match burning marker. I have found that I allow myself 6 matches on a 40+ mile ride and if burn those 6 then I usually am going to be in trouble over the last 5 miles. This has worked for 'me'. I can confirm that if I ride in the 140-145 range for too long, I will be toast after a couple of hours so I tend to try and keep it under 140 which puts me in the 80-90% range of max heart rate.
Like folks have said, it works for some and then not so good for others. I could probably push myself over 150 but I am not going to run the risk unless I am being chased by a dog. I'm averaging around a 100 miles a week and this works for me.
john