What cpu to get?

1. this is your lilsting of yopur build and below what I would change with the reasons why

PCPartPicker part list / Price breakdown by merchant
CPU: Intel - Core i5-8600 3.1GHz 6-Core Processor ($218.98 @ SuperBiiz)
CPU Cooler: Deepcool - GAMMAXX GT 29.5 CFM CPU Cooler ($39.99 @ Newegg)
Motherboard: Asus - ROG STRIX Z370-E GAMING ATX LGA1151 Motherboard ($203.57 @ Walmart)
Memory: Crucial - Ballistix Sport LT 8GB (2 x 4GB) DDR4-2400 Memory ($89.18 @ Newegg)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive ($43.39 @ OutletPC)
Video Card: Asus - GeForce GTX 1080 8GB ROG STRIX Video Card ($595.99 @ Amazon)
Case: Fractal Design - Meshify C Dark TG ATX Mid Tower Case ($88.99 @ SuperBiiz)
Power Supply: EVGA - SuperNOVA G3 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($89.99 @ Amazon)
Case Fan: Deepcool - RF 120 (3 in 1) 56.5 CFM 120mm Fans ($41.86 @ Amazon)
Case Fan: Deepcool - RF 120 (3 in 1) 56.5 CFM 120mm Fans ($41.86 @ Amazon)
Monitor: Asus - VG248QE 24.0" 1920x1080 144Hz Monitor ($229.99 @ Amazon)
Total: $1683.79
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-18 07:30 EDT-0400


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.

PCPartPicker part list / Price breakdown by merchant
CPU: Intel - Core i7-8700 3.2GHz 6-Core Processor ($298.99 @ SuperBiiz)
CPU Cooler: Deepcool - GAMMAXX GT 29.5 CFM CPU Cooler ($39.99 @ Newegg)
Motherboard: Asus - ROG Strix H370-F Gaming ATX LGA1151 Motherboard ($132.64 @ Amazon)
Memory: Crucial - Ballistix Sport LT 8GB (2 x 4GB) DDR4-2400 Memory ($89.18 @ Newegg)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive ($43.39 @ OutletPC)
Video Card: Asus - GeForce GTX 1080 8GB ROG STRIX Video Card ($595.99 @ Amazon)
Case: Fractal Design - Meshify C Dark TG ATX Mid Tower Case ($88.99 @ SuperBiiz)
Power Supply: EVGA - SuperNOVA G3 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($89.99 @ Amazon)
Case Fan: Deepcool - RF 120 (3 in 1) 56.5 CFM 120mm Fans ($41.86 @ Amazon)
Case Fan: Deepcool - RF 120 (3 in 1) 56.5 CFM 120mm Fans ($41.86 @ Amazon)
Monitor: Asus - VG248QE 24.0" 1920x1080 144Hz Monitor ($229.99 @ Amazon)
Total: $1692.87
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-06-18 07:36 EDT-0400
 


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 :)