Jane-
I am a lot like you whereas I feel when doing cardio, that I should be getting about 45 min- 1 hour on my cardio days. In a week, I usually do 2 days all strength, 2 days all cardio, and one day strength and cardio (CircuitMax is a great one for this). Anyway, I have the CTX series and what I usually do is mix two of the cardios from the series together in a day, without doing the weight work or the ab work (ab work is only on a few of the tapes). I personally think that the ab work on the CTX series is good, but not as intense as the ab work on some of Cathe's other tapes (i.e. BodyMax, MIS) So anyway, I mix & match them in different ways depending on how I feel that day. I LOVE the Kickbox tape, so I will usually do Kickbox with 10-10-10, or Kickbox with Power Circuit, and so on. I will start out with a stretch from only one of the videos, and when I move on to the second video, I have it already fast-forwarded to start right after the stretch. When I'm done with the cardio, I always do ab work from one of my other tapes, such as the ones listed above. I personally like BodyMax's ab section. Very intense!! After that I do a stretch from whatever tape I want, but I usually just do the stretch from whatever tape I used to do abs.
Since all of the CTX cardio sections are all almost half an hour long, when you mix two, you've got almost an hour of cardio to do. But I do agree with everyone else on this post that most of them are pretty intense. A few of them start off a little slow, but they will have you sweating and panting by the time that 25 minutes is up.