When I was a decent (15:30s 5k) runner, my RHR was around 52-55. I then moved to Park City and a few months later to Salt Lake City. I was running quite a bit more than before (70+ mpw) and taking my RHR every morning, by counting the pulses for a full minute. Within a few months in SLC, my lowest recorded RHR was 42. With a modern watch taking instantaneous measurements, I'm sure I would have been in the mid 30s at some point.
I quit running about a year later, took 6 years off, gained 40 pounds, and started running again. Within a month my RHR had dropped from 65 to 48. I was living at sea level at the time, so I'm not sure that altitude living has a huge effect. I'm also not someone with a low max HR, my max at this time (age 35) was 200+.
Now, 20 years later, I've just started doing cardio after 8 years of doing nothing at all, and 50 pounds overweight. I was at 72-75 when I started, and 1 month into it am back to 58. I doubt I could run a 7:00 mile today.
I don't think there is a huge correlation between a low HR and times/talent, but I never really trained correctly (constantly way overtrained), so I don't know. I feel that with proper training I'd have been more like a 14-14:20 guy.