Sorry im kinda out of it yes i do plan on using virtual machines Mac os x and ubuntu probably not all at the same time tho
I'm pretty sure the Mac doesn't allow >DDR3-1600 (if not DDR3-1333) and the BIOS is locked-out, so I assume this is a Hackintosh. Unless you have an IB CPU I really don't recommend >DDR-1866 (DDR3-2133 max) on the SB and even then the gains are very VERY minimal especially in ANY form of Virtual Machine. I'd be more interested in 'more' GB than slightly 'faster' frequency with added burden of instability. So IMO DDR3-1600.
The i5-2500K is "DDR3-1066/1333" so correct unless the BIOS allows for access to 'DRAM Frequency' or 'Memory Multiplier' than anything >DDR3-1333 is a waste and quite often a problem running so far below Rated Frequency with such a high Rated Frequency. Simply said DDR3-2133 will run like crap. The 'FSB Ratio' doesn't apply to newer CPU's. Also, IF the chipset is not P67, Z68 or Z77 then you cannot OC the CPU.
The BIOS however 'should' read the CAS correctly so DDR3-1333 CAS 7/8 is indeed faster than DDR3-1333 CAS 9/10.