Most of my "training" is indoors. When I ride outdoors on the weekend, it is usually longer tempo rides with buddies for fun. I am a big fish in a small pond with this group so I can usually dictate the pace. In this over/under workout, you are still riding two relatively long intervals (12 minutes). During the winter when I was really focused on FTP base building, I was doing more SST 2 x 20s. If you look at what SOT was doing during the tail end of his It's Killing Me thread, he was "pulling" his FTP by spending some time above FTP. it worked for him.
I will tell you, these shorter harder intervals do drop down the 2 x 20 averages once these types of workouts are thrown in. I seem to need a longer recovery time than a traditional 2 x20 SST workout, and have a harder time keeping it in the higher range of the SST if I throw a 2 x 20 in the mix too soon after a hard over under. For example, I really struggled yesterday trying to complete two SST 20 minute intervals. I am also doing a lot of bodyweight pistols as part of some other fitness goal I am working on, and I think I am a bit overtrained.
As I said, a big part of my goal is to get the maximum benefit in basically three one hour weekday cycling sessions and some bonus time outdoors on the weekend. My obstacles are work time, family, and my macho desire to try and still do regular strength building workouts. I have basically switched over to a bodyweight routine (as opposed to weights) but it still takes its toll (as does the cycling affect recovery and progress in the strength building).