The 2500k says it supports 1333Mhz ram. And Ivy bridge will support 1600Mhz ram. What does this actually mean? - Surely If your motherboard support ddr3- 1600 you should be able to run your ram at that frequency.
Or is it specified in regards to the onboard graphics of the cpu ? - as in the frequency with which it can swap textures from ram.
Also, will I see any difference between 1333 or 1600 Mhz ram? for gaming only.
Officially the 2nd generation Intel® Core™ only support DDR 3 1066 and 1333 in socket 1155. While you can put DDR 3 1600 and you may have to set it to run at that speed in the bios it really isnt a big issue. The biggest thing with the 2nd generation Intel Core processors is making sure that the memory that you are running is at 1.5v ±5%. Right now I see very little difference in pricing between DDR 3 1333 or 1600. After the 1600 the price does start to run up quickly.