According to the i7 860 specifications page, the memory types are DDR3-1066/1333 which indicate that using more than 1333MHz would probably be unwise.
Using components incorrectly beyond or outside their specifications can and will cause unnecessary problems, resulting in repairs which will end up costing you more money than you may have budgeted.
Either click or copy and paste the following URL into your web-browser's address-bar and press "Enter" http://ark.intel.com/Product.aspx?id=41316 This will take you directly to the info you were looking for.
I hope this will be helpful to you.
Message was edited by: Mikey12