I have been doing The Firm Tough Cardio + some of the harder, longer videos (I just tried Cathe's MIS and love it). I am wanting to get the hardest, best cardio(step) tape of Cathe's, but am confused on all of the choices. I want to bust my butt, and I love to feel a little soreness each morning after. Can someone please tell me which video to get? I do the Advanced Tae-Bo tape once a week (I'm not too interested in kickboxing, etc.)along with MIS two days a week and the Firm 3. I would like to replace two of my "Firm" days with Cathe. The harder the better. Thank you!