Ok, the lack of responses has driven me into further research -and into reading further into the HRM manual. 160 bpm is way too fast for an endurance, or "long" run. Now my HRM beeps whenever I go over 145 or under 125! Which, I must say, was a little annoying on my hilly morning cycling commute today.

I think I "fell" into that pace because of the plan I used to get back into running: several months ago I started with 1-minute run/walk intervals, then eventually worked up to running 30 minutes straight. Not surprisingly, the first time I ran a full mile, the pace I was used to was pretty speedy. Which of course felt good- the speed was an ego boost AND it really doesn't bother my knee like slower jogging can.

Now that I'm running 2-4 miles, 3 days a week, and I've got one 5k under my belt, it makes a lot more sense to ease up on any days I'm not doing sprints/intervals or a race.

As for the knee bothering me at a slower pace, I suppose it's better to build tolerance in the knee than to abuse my heart, and it sounds like I'll get better returns on any future races, if I follow this plan. I ran slower just yesterday, and my knee didn't bother me much.