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?
Where are you seeing performance issues? As your issue might be less with your CPU and more with storage or some other bottleneck.