For me, spinning is much more effective, but the cadence will determine how fast I breathe. I have to try to keep my breathing under control because I have EI asthma. Anyway, I normally maintain a cadence of 86-90 when I'm riding. That is manageable and comfortable for me. When I spin faster, or try to maintain that cadence up a hill in too big a gear, my legs burn and I run out of air. I keep shifting down, trying to maintain about 85 without hurting my legs too bad. On the big hills, I end up in my easiest gear and still can't maintain a cadence of more than abut 45.

My max HR (so far) is about 185 and I hit that sometimes going up the Ugly Hill at the end of my rides... And I always have to stop and catch my breath at the top.