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Have you tried disabling Turbo Boost with Turbo Boost Switcher? I heard that sometimes helps.

http://tbswitcher.rugarciap.com/

I'm looking at buying your exact model. How has it been running for you?
Running like a champ. Our older 2013 imacs have been horrible from the get-go but we are very happy with our 2 mac minis. Hubby runs the same as mine with 512 drive and 16 gb memory. He uses McDraft and Mac Cad and says no issues, smooth sailing. I’m running Filemaker Pro, Final Cut, Calibre, 4 different browsers. No issues. I fired up my Windows 7 machine with 16gb/quad i5 and lordy it is slow, slow, slow.
 
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