Is upgrading my CPU worth it?

Yes it is http://www.asus.com/Motherboards/AMD_AM2Plus/M3N78VM/#C... It is a good upgrade to get the last bit of value out of your system.

Thank you, I will go ahead and do this upgrade then. I'm convinced I have a severe CPU bottleneck going on in certain games, as lowering graphics settings doesn't seem to help FPS or performance, hopefully this will help.

It should, the slow clock of your first gen Phenom being the biggest issue.

The Phenom II x4 965 requires PCB 1.02G. Pretty sure the revision number is located under the PCI-E slot, but my video card is a major pain in the ass to remove in my case. I would like to avoid this if possible; is there any way to find the PCB revision via a serial number or any other means? I would really like to avoid removing the video card if possible.

I can get a Phenom II 940 or 945 regardless of my revision number, but they're difficult to find now at a reasonable price.

Also, the 955s under my Mobo compatibility list have some conflicting compatibility reports by PCB number. http://www.asus.com/Motherboards/AMD_AM2Plus/M3N78VM/#C.... Would be interested in a 955 also, but can't figure out if it's compatible or not.

The upgrade is definitely worth it.

It says that the 955 is supported by all PCB version but the 965 1.02 maybe CPu-Z will display your version. http://www.cpuid.com/softwares/cpu-z.html

I'd advise looking into getting an athlon x2 555 if you can find one for cheap. You can look at the parts number on it and most can unlock to 4 cores and overclock just like a 965 can.

1st, there is no such thing as an unlockable athlon x2 555. Maybe you mean Phenom II X2 555. Yes it is unlockable but not in his motherboard... He is better off with a true quad core.