Ken,
I've never used a rear brake, but think the one case it may be good to have is if one does like push ones spin to limits downhill, that getting the bike back into control with a rear brake at high speed/spin is safer.
I am also intrigued by your going faster at 72 vs. 82. I used to use only 75 and now 85 and find I can ride faster and faster longer with the extra 10.
Al