Performance AND good quality - tweak
SOURCEThis will maintain most of your current ultra settings,
but lower a few settings for a major performance boost. Note, this is designed to improve performance from ultra (highest) settings, in case you either want it to look different, or perform more smoothly.
hdr = 0 (Seems to lower color de-saturation of units, but also removes most of the glowing on most units. Also reduces but not completely eliminates the glossy/shiny look on models)
parallaxshadow=0
shadowmapsize=512 (shadow detail. You can also try 256 or 128.
softshadows=0
softshadowTaps=6
transparentshadows=0 (Major change for ATI Radeon cards I hear. cloaked units get normal shadows instead of transparent.)