AMD Athlon II X4 640 Processor Review
 

Now, if you already have the last generation Athlon II X4 635, then I suggest you keep it. It's not worth paying extra for a little performance increase. Now if you are looking for a solid, low cost, quad core for your HTPC or workstation, then you cannot go wrong with the Athlon II X4 640 processor. At that price, you could build a complete system for what one of the more "high end" CPUs go for.

http://www.overclockersclub.com/reviews/athlon2_x4_640/