Make sure you take black_zion's advice into strong consideration, because the software must be appropriately coded for amd drivers to have good crossfire scaling in the first place.
Something we all tend to ignore or forget, myself included.
Or send a form to amd driver support. and let the guys know of this.
Use and mess with radeonpro, and see if it can help you enhance your framerate or scaling.
gigabyte X58A-UD3R rev.2, core i7 975 3.9ghz (stock voltage), windows 8.1 64-bit, corsair 12gb DDR3 1600mhz 7-7-7-20 RAM, sapphire HD 6990 (stock clocks), coolermaster ultimate 900w PSU.
amd catalyst 14.6 RC2 june23