Question Intel Core 2 Quad Q6600


GPU compatibility is power supply/motherboard. Most likely, something like a 650 Ti is the most recent GPU that makes any sense, but you've told us nothing about your PC other than your CPU, your needs, or your budget.
Could you tell us more about your system? MB,RAM,PSU,HDD Monitor. It's possible the MB chipset has Graphics. That's how it was often done back when that was current. You may have a lot of better CPU options available for little money, or a free overclock to 3Ghz.
Also which version of Q6600? SLACR is the good one, SL9UM not so much. Without knowing more i would suggest a GTX1050-2GB and at leat 6GB RAM. The 750Ti and GTX1050 usually don't need a PSU upgrade.
Feb 16, 2020
Windows 10 Pro 64 Bit
CPU: Intel Core 2 Quad Q6600 2.40ghz
Ram: 2GB DDR2 800mhz and 1GB DDR2 800mhz
Mobo: G41M Combo
PSU: AC/220V dunno how watts does it has i think 450watts
The G41 MB should support the tapemod to 3Ghz if you have the SLACR version of the Q6600.
The 2nd photo is the mod.

It should also support Q9650.Q9550 CPUs which will outperform the Q6600/3GHz and have some newer instruction sets to run more modern games.
Another option would be a tapemod E7500 2 core at 3.67GHz.

8GB DDR2 800 is hard to find 2x4GB low density(512x64) modules at any kind of reasonable price. But they do exist.
Buffered,ECC, or 256x128 won't work.
If you can reach that level then a GTX1050-2GB would work. Or even a GTX10603GB.

I have a Dell Optiplex 380 G41 with an X5470 3.3Ghz Xeon swap 8GB DDR3 and a GTX1060 3GB.
The tapemod E7500 ($6) outperforms my Xeon in single thread apps. (like games).