Everquest won't run on a CPU > 4.2ghz, you have to underclock it to run at below 4.2ghz. If you're familiar with AMD Overdrive you should be able to setup a profile for specifically for EQ to run it at a lower speed.
Edit: These threads might be helpful for you:
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https://forums.daybreakgames.com/eq/...please.212991/
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http://www.eqemulator.org/forums/sho...t=37521&page=4
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http://www.eqemulator.org/forums/showthread.php?t=36707