Please take a look at Alex Tinsley's response to the following question in our PreSonus Answers system.
If you take a look at the following statement, you will understand the importance of the processor speed in general.
"you don't benefit from multi-processing in a song with a single track with a large number of effects, however you do with multiple tracks and virtual instruments. "
That being said, you need to have the high CPU speed for use with individual audio tracks that use a large number of effects. If you are working with extremely large songs that use virtual instruments, then you may want to lean toward the higher number of cores for the processor. Both are important. If your processor will run at 3.6 Ghz. natively, then you may want to go with the higher number of cores.