Odd question because there are too many variables. "Rimshotter" is a vague reference. There are examples of stations out 40+ miles from the target center that can technically be heard and may be rated, so depending on the goal, could be considered a success. Ultimately though, field strength always wins. That's just a fact.
If you're primarily running mono programming, you should always turn off your pilot and operate mono. Even in the market and especially with terrain shielded places, running stereo you always run the risk of listeners experiencing either the effects of multipath worse when the station is running stereo. The multipath is never worse in stereo as some have alleged, but it can be more pronounced sounding, depending on the receiver.
Technically and according to the antiquated rules, you're supposed to run mono during mono programming anyway. That said; nobody ever got an NAL for running stereo with mono programming.
