I suggest that you try running or doing any physical activity at that elevation to see what that PPO2 means. FYI, I am speaking from experience: I ran a mile at my top speed loaded with gear at 11,000ft, which is lower than Mt. Blanc. In retrospect, it was a bad idea. The headache was terrible and I was about to pass out. That happened when I was 25 and in the top shape.
There is no reason to screw around with dil changes as you come up. Choose your gas mix properly, then flush with O2 at 6m or shallower.