Actually I've never ridden with a cadence meter and am pretty much guessing. Judging by my watch now and then I know what 90 feels like (and I didn't used to ride with a watch). If I'm hitting what feels like 100 plus I'm probably going too slow and move up a gear. I probably don't go down to 70 except when I'm in the middle of an inhabited part of the mup or just checking scenery and that's not on a heavy gear.
I've never been much of a low rpm masher on flats but the hills are affecting my knees nowadays. That's why I'm trying out the compact next season.