Just some casual gaming and my pentium cpu couldn't cope with my graphics card and Cpu usage in almost every game hits 100 and never got the fps which the card can deliver
"casual gaming" has no meaning in this context. It ain't like others are wearing a dinner suit to play...
Something like "I'm trying to play the latest triple A games at 60fps+ at 1080p " would be the kind of info you'd need for someone to answer you.
A retro gamer looking to get the best from Mame would get a different answer. As would someone struggling with a PS3 emulator.
With upgrades, you ideally want to know it will be enough to achieve what you want rather than just being better than what you have now (but still not enough).
If the new CPU and / or your current gpu is still insufficient for the intended purpose then the upgrade would be a waste of money. I am personally guilty of wasting a whole lot of cash while trying to save myself money by cheaping out....