CPU of Track Instruments Vs. Rack Instruments and PLAY

I have done some testing on big projects using East West Play engine and compare track instruments vs. rack instruments. The result I got was that using track instruments I used more CPU, but there were less clicks and fall outs. Using Rack instruments I had better CPU but more clicks and fallouts. I think it’s quite contradictory, more efficient CPU but more fallouts. I also know that instances of PLAY gets spread out over all the cores, so that’s why I thought maybe instrument tracks would be more efficient. Can somebody explain?