I've never been a fast climber on my single. When I do climb on a single, I'm usually out of the saddle, 70% of the time, especially when the grades go double digit. 4-6 MPH, usually on steep and extended climbs. That's my zone.
Since I started riding tandem last summer, I've noticed just we achieve just about the same speed, maybe slightly less.
So, what speeds are most of you seeing when climbing?