Did you mean an i5-8400 instead? As there is no i5-8700 - that's an i7, which would have the same number of cores as the 9700.

The i5-8400 would be fine for most IT homelabs; there are some specific applications that really need more power than that (especially any of the Cisco bits from what I've heard, but I have no first-hand experience with those).

What exactly are you planning on doing with the homelab?

I’d think many of us have large amounts of mostly idle cores. 🙂

If I were to start from scratch, I’d pick something power efficient first.

My home lab attempts to duplicate much of what I use and support at work. As such, I have many VMs, each with a particular purpose or running a particular piece of software. So, for me, it's a combination of more cores and decent speed of each. However, in virtualization, it's common to run out of RAM in a host before you run out of processing power.