Some current games already show a performance benefit with more than 8 cores. Unless you want to be behind the curve, 8 cores, 8 P-cores, should be the absolute minimum to aim for, for max performance in a new system you plan to keep for 5+ years.Though for now and probably for a while for high their gaming and not doing background tasks even 6 cores can cut it and 8 is more than enough. More probably not going to do anything for a while as SMP programing with games is like almost impossible that it seems making use of more cores gets so hard. The jump from 1 to 2 and 2 to 4 were easy. But jump from 4 to 6 and beyond games just struggle to use so much.
So faster and faster IPC gain 6-8 core CPUs at least for now are best for gaming assuming no intensive background tasks. Though high end gaming build 8 core slight overkill is best.