In my 2nd account, 4S PvP started to appear when my T5AP is about 2500 and Regimental Rank 18.
My current 4S range from 171T to 176T. It can be tough depending on your army combo as well as map conditions. For example, if you've mainly range regiments then when you come up against AI melee regiments in certain map, double RoF is not enough to hold them and you may need to rr. A strong AI GG can wreck havoc as well.
Tough 4S PvP are not at endgame but rather at lower AP and Regimental Rank. Fielding an army of 4* Rank 22 equipped with Legendary & Epic items going up against 3*/4*/5* Rank 22/23 AI regiments and winning is very good for my ego. Lots of fist pumping moments.
