I suggest testing framerates with both pc's naked, as in, no addons, then that will eliminate any thought of it being an addon, and if they are identical, then you may have to check in to AA, addons anonymous, it's ok, I've been there, great people
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Also, addons like recount, LAG if you don't reset the info on them, they keep all their stuff and it causes just an immense amount of lag, especially in raid situations.