If you're not thinking about going faster, I don't think of fewer teeth up front as a way to limit cadence: cadence in your situation is a red herring. Cadence isn't your limiter, it sounds like HR is your limiter. A smaller chainring is a way to allow you to go slower while still balancing. Depending on your medical condition, you're trying to keep your HR below 130 max -- how close do you come to this on those sustained 8% climbs? Since a lower gear allows you to go more slowly, you'll gain a little margin of error (about 5%) in keeping your HR lower. That 5% difference is *roughly* like getting another rear cog that's a couple of teeth larger (and sort of making your smallest cog the equivalent of about half a tooth larger). If you're *not* bumping up against your max HR, then there's not much to be gained (or to be lost) from switching, but the decision isn't about the *average* effect (which is kinda small) but at the margin (where it can be more important).