This is really cool and I admire that you're doing it. Good luck getting ready for a race!

I can currently do 5k on a treadmill at 3.2 mph, but I have no interest in racing or really in going much faster than that. I'm in it for the general health and lifespan benefits, plus I find it meditative and pleasantly tiring--going faster would tend to ruin that by making me pay more attention to my body and less to letting my mind wander.