My guess is the 8600 as the 8400 is slightly better then the 7700 and with the higher stock/boost speed the performance would only be better on the 8600.
The 8600 is a six core CPU, so I would put money on the 8600.
yea unlike Kaby Lake Series
Intel i5 8600 wil not doubt beat the i5 8500
Putting Price out of the way, and look at the performance.
People Choose Intel i5 7500 over i5 7600 (Obiviously i5 7600 is at Max Performance of that Generation of i5.