CPUID CPUz will tell you the cpu and chipsets used. from there you can lookup what those chipsets support. most modern day CPU's have integrated memory controller.
the i7-870 has integrated ddr3 memory controller which supports ddr3-1066 or ddr3-1333, however, intel site doesnt say if 1333 is clocked down to run at the slower 1066 speed, you can call Intel and ask. i7-870 is a heat monster..... http://ark.intel.com/Product.aspx?id=41315
but since you have 1333 you can just buy more 1333, unless you are needing more ram, then you need to do some research to find the best ram, etc. if the CPU clocks it at 533MHz and you find ram that has lower CL then your 1333 then getting 1066 with better CL would be a better choice (but will cost you more if you are needing to replace your existing 1333, etc)