i haven't seen it posted so i thought i would add it
-nologs -nosplash -world=empty -CPUCount=6 -exThreads=7
(6 being the number of psychical cores your processor has)
exThreads mainly. 7 pertains to dividing Geometry loading, Texture loading and File Operations in to there own threads.
i saw an improvement when i added that to the steam launch options.
also just taking time setting up all the video settings helps too...rarely is ultra an vast improvement over high.