X99 will be LGA2011-3 not backwards compatible with previous LGA2011 processors. These are 'workstation' class motherboards but they can be used for gaming. They offer several advantages over LGA1150 boards, more PCIe lanes, and quad channel memory. No real impact on gaming if you use a single or even two video cards. More for the people who want to do 3 and 4 video cards.
As with every new memory release the memory available now is technically faster. It will be a while before enthusiast memory catches up to the early adopters.
DDR4 looks like it will release with a base speed of 2133 with a CAS of 15, you can get DDR3 2133 with a CAS of 10 now, Or on the extreme side of things DDR3 3000 with a CAS of 12.