If it were me, I'd a least buy a Z270 on sale so you have the option of overclocking in the future. I don't currently overclock my CPU either because it is still fast enough, but maybe in 3-4 years I can get a little extra performance out of it if I want to.
What always happens with Intel boards since they change sockets pretty often, is once they go out of production, within a couple of years it gets harder and more expensive to find one. And then you are stuck overpaying for a used one on Ebay.