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

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?