I currently have an i5 6600k cpu with a Cooler master hyper 212 evo heat sink. I am considering upgrading to an i7 9700k cpu. I get that when over clocking a lot I would want to consider something better probably, but by default, will it be much hotter than the previous one?
The 6600k uses @ 75w at stock. The 9700k uses @ 200w at stock.
Guaranteed the 9700k runs hotter.
The CM hyper212 evo is a 140w cooler. So it'll not handle anything more complicated than websurfing or that 9700k will thermal choke and end up shutting down. You should be looking at 250w+ range coolers such as most 240mm aios or larger, or the big air coolers such as NH-D15/S, beQuiet Dark Rock Pro 4, Cryorig R1 etc if you want to keep gaming temps under 70°C