I have only done the Sweating Buckets (Team Clydesdale - 45 min), Climbing (Leadville - 1 hr and 10 min) and the Iron Girl indoor (about 30 min each) spinervals. So my comparisons are a bit limited. My biggest weaknesses are standing and climbing (overweight), so this is where I am coming from. Sweating Buckets was a challenge for me when I first started. So I would call it a low to medium challenge for a cyclist who has been riding a bit. The 3 Iron Girl workouts are more intense, but shorter in length. Each one has a little different slant. They are still a moderate challenge to me because of the standing recommended and the one called advanced is a high gear one that really gets my heart going. Of course, Leadville is a huge challenge for me as it simulates climbing. The standing is mostly doable and realistic. The high gear intervals (some lower included too) is also a challenge not only because of my weight, but the length of the session. They each have their place and I try to mix them up with Leadville only making the rotation about every 6 weeks, but I am getting better.

Hope this helps.

P2