Speaking from experience, stay far away from the 820. It is borderline infuriatingly slow, and any of the touchscreen "gestures" like swiping between data screens are executed slowly, if the input isn't divorced from computer response entirely. Typically the defining feature between the 530/830 is the more robust/feature-complete navigation on the 830, so maybe give that a ponder since a new 530 is priced pretty near the Amazon 820? Both the 530 and 830 have the same sized screens, which checks that box for you, and while a touchscreen is a smidge nicer off the bike, I'd prefer buttons while actually riding (starting/stopping rides and switching data screens).