I ride out west from D.C. to a nice rural area west of Middleburg, Virginia. Nice open roads with long straights and fun twisties. A bit of a PITA to get to from my current home inside the Beltway, but once I'm there, I can spend all day back and forth on farm roads doing all my necessary, ummm, "testing."
(But in all seriousness: it's also been my "proving ground" when I need to tweak my Juicebox settings manually, usually around the changing seasons. Plenty of open space to go flat-out from a standing stop up to a
very generous speed to test out performance in all the gears. Rinse, repeat :thumbup

.