Performance or Pace-time?

I have been following a few training logs here and I note a heavy emphasis on "race-pace" training with ample recovery time. I have to assume this works well since the people posting are swimming far faster than I. so here is the question: when performing a high intensity set like that, is the emphasis on maintaining the speed, taking as much recovery time as you need to keep up the speed, or should you maintain the selected turn-over time and struggle to maintain the speed in the face of increasing fatigue? If you are finding a pace too steep to maintain the speed, do you slip to a slower pace, or should you just take a break and restart the set at the same pace after a bit of recovery? I am specifically refering to speed sets done at 90 percent of race-pace or better. The same question should be applied to stroke technique: as I fatigue my stroke tends to break-up a bit (Ok: a lot). In training should I select paces that allow me to always maintain a "perfect" stroke, or should I push into the "red zone" where I am fatigued enough that my stroke is getting ragged? BTW: my "ragged" stroke is quite a bit faster than my technical stroke, but it really is quite "splashy". My daughter actually calls me "Dr.Splashy" when she teases me.