I usually don't try to do the circuits as fast as possible, only aiming to finish the whole workout within and hour and a half or so. Sometimes I will go through them pretty quickly, though. That type of training is taxing, but satisfying. I've made the mistake of trying to include heavy lunges in circuits before, which has the potential to put you on your ass.
An example workout would be: snatch pulls to snatch-grip deadlifts (as weights increase). Then maybe a circuit of dips, rows, one-arm dumbbell push presses, and cable crunches. How much rest I take between each varies a bit, but I try not to take too long. I rest more in the supersets than in the ciruits, usually.
I usually end up doing two supersets of two or three exercises instead of a single circuit. Also, if the main compound exercises are less taxing, then I'll include those in the supersets. For example: Front squats and barbell overhead press, then RDLs and bent-over straight-arm cable pull downs, then cable rows and side pulls from a low cable pulley (for obliques). Yesterday I did power snatches and snatches, then supersetted RDLs and pullovers, then RDLs and straight-arm pulldowns. I usually do a bit more than this each workout, but didn't want to wear myself out on New Year's Eve.
Also, I think that good mornings do hit some different muscles than the RDLs. I will do both (but probably more RDLs). I think that my issue may have been that I wasn't spreading my hips (ie. pushing the floor apart with my feet). This resulted in my using my lower back too much, instead of supporting with my hips/glutes. That's why I did so many of them yesterday. I also noticed that my snatches were a lot better when I concentrated on doing this. I don't think you can really get a full extension of the hips without it, and just end up hyperextending the back and lifting with the arms.