First, I think 95% is too high for most athletes in an Olympic. I tried that for years. I went to about 90% and was overall much faster at the finish line.

Second, how much do you vary? Not much. You basically want to go a little higher power when you are going slower and a little lower power when you are going faster.... but two things get in the way of large variability. 1. The slower portions take more time. 2. Going 5% under for 3:00 does not provide all the recovery from going 5% over for 3:00.... or as the Brits say, " you never make up on the straights what you lose on the roundabouts."

Vary you effort less than you think to get the fastest time.