Not all CPU's of the same name perform identically. They vary. And yes, if you want to overclock you need to increase vCore at some point.
Some crashes are RAM related. Depending on the system, when you overclock the CPU you are also overclocking the RAM. You may need to drop the frequency of the RAM before overclocking.
For example, I dropped my RAM from 400Mhz to 333MHz. I then managed to overclock my CPU by 20% so my RAM is back up to 400MHz. They share a common reference clock.
Another tool is the Task Manager (CTRL-ALT-DEL). Run this while playing a game for at least 5 minutes. If the CPU never hits 100% (you can see its history) then you are limited by your graphics card and further overclocking your CPU will make no difference.