Performance/ Standard Cores

I don't remember the technical terms here, so bear with me.  I have a Precision 3660 I9 with 24 cores.  I have software licensed for 16 cores but come to find out if you run with all cores on in the computer, performance is terrible- something about it only runs as fast as the slowest core.  We have since turned off all but the 8 performance cores and performance during analysis is much better.  Is there a way to better utilize what I have, or is it a lost cause unless I have a computer with 16 performance cores to work with?