My Gigabyte EX58 UD5 also supports DDR3 2100+/1333 as does their Extreme EX58 board.
All it means is you can use any DDR3 core i7 memory in duel or triple channel in 2,3,4,6,12gig-24gig capacities and you can use rated speeds from 1333mhz right up to and over 2100mhz DDR3 ram.
For example I have Corsair Dominator 1600mhz memory in mine. All I did was going in and tell the BIOS to load the memory XMP profile 1. The BIOS then upped my ram from the 1333mhz it first booted at to 1600mhz which is what mine is rated for. The process would be the same if you bought 1800mhz or 2000mhz RAM.