While I would normally say that that is a downgrade, not an upgrade (due to my extreme prejudice against all things Pentium), I'll give actual feedback instead: it isn't an upgrade, but more of a move to the side, as that chip doesn't beat your current one (more GHz != better). Also it's a 45nm whereas your current one is a 65nm (assuming it's the Intel Core 2 Duo E6600 I think it is), which means your motherboard may not be compatible.
If your current motherboard is an LGA 775 65nm mobo, it probably doesn't accept DDR3
Thanks! This is the kind of knowledge I lack. The supported CPU info on my mobo is Socket LGA 775, Type Core 2 Quad / Core 2 Extreme / Core 2 Duo, FSB 1333/1066MHz. Didn't see anything that would allow me to "match" whatever the nm is between CPU and mobo, although it looks like it's important, even if they're the same socket type.
If more GHz doesn't mean a better CPU, what does?
I looked up my motherboard and yep you're right about the RAM. It says its "memory standard" is DDR2 800.