Hi there,
I must also agree that High Step Challenge ranks up there as one of my all-time favorite Cathe DVD's, particularly in the circuit training category. IMO, it is already very intense as designed. I often times find it a challenge to make it through the entire workout without pausing/stopping. I love this workout and can't praise it enough! My favorite cycles are 1-3 in this workout, probably because they're the ones that I do most often - LOL. I like the music and the energy of the cast in this one too.
Over the years, I've really played around with the workout intensity, especially after doing the 1RM tests for STS. I really bumped up the intesnity by lifting the heaviest weights that I could for exercises (i.e. use my smith machine for the squats, barbell lunges, etc), and WOW - what incredible results to an already comprehensive program. My point in this is that this workout has grown with me over the 5 years that I've owned it, and it never gets boring. I reach for it often when I workout at home.
Let us know what you decide!
Good luck
fitgirl-atx