Here's another example - the climb I did yesterday. It's a little over 3 miles, 8% average grade. For years, I'd do it in somewhere between 25 and 30 minutes, with my heart rate rising quickly up to about 165, with occasional peaks up to as much as 185 on the steepest pitches. This was when I was both fitter and lighter, as well as about 15-20 years younger.

Yesterday, I did it in 27:45, so about middle of that range. Average HR was 149, and max was 160. So, speed in the same range, but the HR ranges are just completely different.

EDIT: It FELT the same as it used to when I was doing it in the 160-180 range, right down to how it feels going around the 20% switchback.