I think "roll-ons" per se; meaning trying to race without downshifting, is plain silly, if you're really serious about outrunning someone if youy are not already in your powerband then you downshift to get there.
It's simply a test invented by magazines, in the real world no one cruises at 65 in 5th and tries to race from that gear unless they want to lose.
I've raced a guy at work on his 113ci S&S fat bastard chopper he built and I've beat him like a stepchild from every speed in any gear except in 1st, but halfway thru 2nd I'm still passing him.
for some reason those choppers with the fat tires dont run as strong as the ones in a stock frame....its not uncommon for say a 113 to be running 90 hp and 105 tq...its like everything else the tune has a lot to do with it...90 % are way over jetted plus the fat tire on the choppers limit them from what pipes they can run...its more for looks....and as you know the wrong pipe and your way down on power....when doing rollons with another v twin your just measuring how the motor is running the power its making ...then we would change jetting or pipes and go again...better then a dyno its shows whats working and what dont.....as far as down shifting against other bikes i didnt care what gear they where in at highway speed.....mine in fifth pulled better then if i started in 4.......if you wanted to see the power of your max to anothermax...banging gears will tell you nothing except whos the better rider.....get side by side on the highway in 5th and roll it on..the stronger better tuned motor for the street will pull the other ...5th gear gives you a good long look at the power difference