I'm leaning mostly towards CPU, but i could easily be wrong.
Since you've already seem familiar with overclocking and such i suggest an experiment
Stand at a chosen spot in your minecraft world and choose a point to look at, then write down your FPS and log out.
Then underclock (or overclock) your CPU (or just set it to stock clock)
Log in to minecraft, stand at the same point, look at the same thing, write down your fps and log out.
Underclock your GPU with the same % as you underclocked your CPU.
Log in to minecraft etc.
Bring your CPU back to the clock it had to begin with.
Log into minecraft etc.
Looking at the numbers you get from that you should be able to determine if it's your CPU or GPU that is causing the bottleneck.
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