To be fair to what Harold is saying (and I can't believe I actually agree with him on this) SSPD still is better than a Det/Crit build for the simple fact that it gives you more flexibility as far as getting casts off. You don't need to have continous casting for the SSPD build to come out ahead, you just need one span of time where the SSPD set can get a cast off where the DET/CRIT one cannot.

Say for example the SSPD set took 2.3s to cast F1, and the DET/CRIT one took 2.4. What happens when you have a pause for 2.35s to launch a spell? In that case the SSPD set can get a cast off where it is impossible for the other build to do so. That is the advantage SSPD gives, continous casting is only part of it.