I hacked my ‘un-overclockable’ i5 6500 to hit 4.3GHz and outperformed my old i7 2600K

Perhaps we are the same, you and me. Perhaps we both invested in a solid Sandy Bridge CPU in 2011, spurred on by the rave reviews, and perhaps we have both been too proud to ‘downgrade’ to a newer model i5 in the subsequent years for fear of what the other kids in the playground would say - or what it might do to our Cinebench numbers. Well, recently I went for it, and guess what? Going from i7 to i5 increased my PC’s performance. 

Related: the best CPU for gaming. 

CPU upgrades are hard. Buying a new one probably means buying a new motherboard with a compatible chipset, and that in turn probably means new RAM too, so there is a considerable financial and time investment involved. Then there is the fact that CPUs hold their value so well over time. Generally that means it isn’t worth buying anything but the latest models on sale, which further forces your hand into upgrading your whole chipset.

from
https://www.pcgamesn.com/i5-6500-overclock-43ghz