I would recommend the M600 Processor for one major reason. The T6600 does not support Virtualization. This means that if you upgrade Windows 7 to Professional or Ultimate you can not run XP Mode or create VHD. These are advanced features but for the same cost I would want the feature. In my case I bought a Laptop with the T6600 and realized this after upgrading. I sold the T6600 Laptop to a friend and bought the M600. There are other Intel processors that don't support Virtualization so check the Intel site before you purchase.
From AMD.com "All AMD Athlon™, AMD Phenom™, AMD Phenom II, AMD Turion™ and AMD Opteron™ processors shipped by AMD will be able to use the AMD-V™ feature, and subsequently benefit from Windows® XP Mode in Windows® 7"