I'm looking to upgrade the memory in my computer to >=12Gb (for running virtual network images of 2008 server/exchange/sql/sharepoint/etc.)

Currently I have an Asus P6X58-E motherboard with 3 x 2Gb DDR3 1600mhz (8-8-24 1.65v) DIMMs in it. Another 3 x 2GB of the same stuff costs £70 but i've read somewhere that you can't run 6 x 2Gb DIMMS on the motherboard at 1600Mhz and you need to throttle it back to 1333Mhz?

Because of this I was thinking that a better option might be just to buy 3 x 4Gb DDR3 1333Mhz (1.5v) DIMMs instead as it's only £30 more.

Would it work running (3 x 4Gb DDR3-1333) and (3 x 2Gb DDR3-1600) at the same time to give me 18Gb total? I understand that the 1600Mhz RAM will have to run at 1333Mhz but is this possibly on a triple channel X58 motherboard?

Normally this would work fine on a DDR2 motherboard mixing the RAM speeds but I wasn't sure if the triple-channel memory, different voltage and DDR3 memory would be a problem as I've heard DDR3 is a bit more fiddly in getting it to work?

Any thoughts and advice appreciated!