If you're not training for a race, I would ride based on perceived exertion or ventilatory threshold. So basically about the effort to takes to maintain a slow steady rhythm of breathing where you can carry on a conversation, one sentence at a time. You can exceed that effort to get over short hills, etc but generally settle back to the standard or below. I think that would keep your HR in an aerobic zone where the most gains can be made. YMMV.