I love this app as it's the best alternative to MediaMonkey on OS X that I can find. What bothers me is how it's not a native Mac app and it takes up so many resources. I imported in my library a month ago and it's still sluggish. Please see the screenshot.
You do realize that your CPU has 4 cores, and MC is only taking up 25% of one core right? So it's consuming roughly 6.25% of your CPU in total.
My MBP has a quad core i7 and MC takes around 10% (up to 15%) while playing audio. Again, this is of one core out of four.
If MC behaves slowly, Awesome Donkey might be right: You might have background tasks running. Go to: Help > System info . Look at background processes and at percentage of thumbnails built. If you have background tasks running, they slow MC down until MC is done with them. This is really only a first time thing when importing a large library. Once it's done, it's done and MC will run normally.
If you're experiencing audio dropouts, you should increase the buffering on the Audio device:
Tools > Options > Audio > Audio Device > Device Settings > Buffering > Software > (pick at least 250 mS here; 500 is better)
Tools > Options > Audio > Audio Device > Device Settings > Buffering > Hardware > Hardware default
You might also want to see what you have Integer mode set to on this same screen. On some DACs, integer mode causes some audio glitches. If it's on, turn it OFF.
After making all of these changes, save, then stop and restart MC. Good luck!
Brian.