Lowering settings can be counter productive. Fps is all about the cpu, resolution is all gpu. When you lower settings, the gpu has an easier workload, so can demand more fps from the cpu. The cpu can only deal with so much code at any one time, so ends up inching closer to 100% usage on 2 cores, with 2 other cores dealing with windows etc. This maximizing of load on the cpu actually slows things down, so net result of lowering your settings is actually a lowering of total fps as the cpu gets swamped.
Instead, maximize gpu bound settings and minimize cpu bound settings like grass detail, viewing distance, move physX to the gpu etc. This raises the gpu workload, lowers cpu workload with a net result of increasing fps.