Hi, XenaFan! IMHO, Interval Max is much more intense at its peak (understanding that intensity modifications are demonstrated throughout the workout to ease you into it) than Body Max step sections. I cannot really speak to how Body Max compared to Rhythmic Step in terms of intensity, because the speed of the movements and the complex choreography of Rhythmic Step have always defeated This Ole A-jock, thus it is not really a part of my ongoing program except for its warm-up.
IMHO, you'd do best by kicking over the traces and getting the 3-workout DVD - too many people rave about Rhythmic Step for you to pass it by, and the 3-workout combo is really great!
Hope this helps -
Annette Q. Aquajock