Please check this comparison chart:
The difference is really small, since one has slower clock speed but faster cache RAM.
I would suggest contacting an Authorized Intel® Distributor or reseller so they can provide you the best recommendations.
What have you done with the CPU?
And we want to buy a database server with six core processor (around 48GB RAM) and we need advice on choosing good processor (X5690, E5-2667 or E5-4617...)