Race is this weekend or in two weeks? I know you're pretty set on 6:52 pace. Still would suggest going out 7:10-715 for the the first 5K and then maybe drop to 7:00-7:05 for the next 5-10K and work your way down if you're still feeling you got 20 amazing miles in you.
I get it, and know you're pretty fixed on the goal, but if you truly have the fitness, you should be able to build and feel great. Because if you go out at 6:45 and your body isn't feeling it, things are going to be fine for a long time, but around miles 16-20 it's gonna really suck.
Trust yourself, but be honest with yourself.