We're running practically the same systems, and I struggle to keep it steady, on most maps I'll get 10fps for a while then a drop, to 5fps, I recommend a complete fix of your computer + a little updating, and if that does not work, keep to the Minimum settings and generally don't fiddle with them. But take the lag 'spikes' as they come, when the lag comes F3 is the best option, but there a few maps where lag is never a issues.
Hope I have been of assistance.
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