The problem with collecting ancients is how to stop

So now I restarted, I started looking at other copper and bronze coins. Picked this one just because it looked too nice to not pick.

Genius on the reserve is nicely done, but the emperor portrait, having had time with the coin in hand I can see it is a very different art style already.
I think I will try to stick with an emperor face collection of sestertii only.
People who collect the more classical look on portraits, at which emperor do you mark the divide between styles?