1. changes your board from a z 370 to a h370, keeping performance, but since your not using a K cpu you dont need a Z board.
2. using the money saves I upgraded your I5-8400 to an I7-8700
Overall you have a top line pc, and for 10$ more than you had before with no compromise from the previous offering.
So the i5 8600 build can handle any games at 1080p 144hz??
ANY + 144hz is a lot MOST is best I can give you, and you won't get much better either. 8600 should handle ~95% and i7 ~97 % of games.
there are games that just don't play more than 120 fps