Turns out that "certified" speedometer / odometer is pretty accurate... Assuming "accuracy" is determined by whether it agrees with Google Maps. It came up with 1033.7 miles for the trip whereas Google Maps said 1040... About 0.6% lower...
Whereas most motorcycle manufacturers set their speedometers to register slightly lower than the true speed (thus you are less likely to get a ticket), on the FLHP-I, it is very slightly the other way... I guess that's so that if the cop is giving you a ticket based on his speedometer, you would be going more than what he indicated... Still, even with that, you would have to be going over 166 mph before it even made 1 mph difference... If you're going 166 mph, you definitely don't need to worry about that Harley writing you a ticket based on his speedometer... From what I understand, the bike tops out at around 104 mph with the windshield... Of course, the speedometer doesn't go that high anyway...
I've ordered a couple of different cell phone mounts off of eBay to try before my next long ride... I've yet to find a cell phone mount that I would truly trust on a motorcycle... Hell, most of them I don't even trust in my Jeep on bumpy *roads*...