CoffeeBreak9To5

Yeah I can squeeze it in for close to the same price, but both his build and mine would be sacrificing the 1TB of SSD storage in favor of a 240GB SSD and a 1TB HDD. The great benefit to having a larger SSD is that you can house pretty much all your games on it, which has the benefit of huge load time reductions, and in some games reductions in texture pop-in. So with both you are giving that up. On a 240GB SSD you can basically only hold 2-3 big games, and 3-5 smaller games. The performance difference between the 2060 and 2070 is roughly 10% on average. You likely won't notice a difference in most games because you'll be above 60 FPS anyway, but it will make a small difference in Metro Exodus and Assassin's Creed Odyssey as I noted were lower performers above.
 
PCPartPicker part list / Price breakdown by merchant Type Item Price CPU Intel - Core i5-9400F 2.9 GHz 6-Core Processor $174.89 @ OutletPC Motherboard Gigabyte - Z390 UD ATX LGA1151 Motherboard $119.99 @ Amazon Memory OLOy - 16 GB (2 x 8 GB) DDR4-3000 Memory $78.99 @ Newegg Storage Kingston - A400 240 GB 2.5" Solid State Drive $29.99 @ Amazon Storage Hitachi - Ultrastar 1 TB 3.5" 7200RPM Internal Hard Drive $36.79 @ Amazon Video Card Gigabyte - GeForce RTX 2070 8 GB WINDFORCE Video Card $479.99 @ Newegg Case Deepcool - DUKASE WHV2 ATX Mid Tower Case $54.96 @ Amazon Power Supply SeaSonic - FOCUS Plus Gold 550 W 80+ Gold Certified Fully-Modular ATX Power Supply $50.98 @ Newegg   Prices include shipping, taxes, rebates, and discounts     Total (before mail-in rebates) $1051.58   Mail-in rebates -$25.00   Total $1026.58   Generated by PCPartPicker 2019-04-15 22:52 EDT-0400    

Mostly. A notable exception will be Metro Exodus, but not even a 1080 Ti maintains 60 FPS at max settings on some maps, so you won't even do better by going up to the 2070 for that game. Also Assassin's Creed Odyssey, same story. Everything else should largely hit at least 60 FPS at Ultra and should do the same for max as well.  

Yep. That works. If you feel 240GB is doable then go for it. It's basically my original build minus the CPU cooler, a reduced SSD, and a 2070 with the same color scheme. What's not to like?

Only a few fps improvement on average, it's a 2600x but you can oc the 2600 to match 2600x speeds.

I don't cherry pick at all. Here's basically every source on the internet saying the same thing and showing the 8400 beating the 2600x and the 2700x in almost every single game:
 
https://www.tomshardware.com/reviews/intel-core-i5-9600k-coffee-lake-cpu,5922-5.html
https://www.anandtech.com/show/12625/amd-second-generation-ryzen-7-2700x-2700-ryzen-5-2600x-2600/15
https://www.techpowerup.com/reviews/Intel/Core_i5_9600K/13.html
https://www.pcper.com/reviews/Processors/Ryzen-7-2700X-and-Ryzen-5-2600X-Review-Zen-Matures/Gaming-Performance
 
These results are from Tom's Hardware, AnandTech, Tech Powerup, Pc Perspective, all well established and credible sources.
 
That result you're talking about with the Pentium performing identically to a 9900K DOES make sense because the game was 100% GPU bound where the GPU was bottlenecking all of the CPUs and hence they ALL performed the same. This happens in a few games out there, especially when resolutions get higher.
 
I'm sure if you tested Witcher 3 at 8K every processor on the planet (I'm exaggerating) would show the same performance.

As Luke has pointed out it only happened with the 2080 Ti and some other more powerful cards. SeaSonic is rectifying the issue for any users experiencing the issue and most of the pre-2018 models are not in stores anymore.
 
On these very forums it's still a tier A PSU and in this build it will not be an issue.

The PSU known for random shutdowns... uh, no thank you. (Source)

I have just the build that checks off all your boxes, including theme:
 
PCPartPicker part list / Price breakdown by merchant Type Item Price CPU Intel - Core i5-9400F 2.9 GHz 6-Core Processor $174.89 @ OutletPC CPU Cooler ARCTIC - Freezer 33 eSports Edition (Black/White) CPU Cooler $47.11 @ Newegg Business Motherboard Gigabyte - Z390 UD ATX LGA1151 Motherboard $123.98 @ SuperBiiz Memory Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory $87.99 @ Amazon Storage Intel - 660p Series 1 TB M.2-2280 Solid State Drive $109.99 @ Newegg Video Card MSI - GeForce RTX 2060 6 GB VENTUS OC Video Card $349.99 @ Newegg Case Corsair - SPEC-OMEGA ATX Mid Tower Case $69.99 @ Newegg Power Supply SeaSonic - FOCUS Plus Gold 550 W 80+ Gold Certified Fully-Modular ATX Power Supply $50.98 @ Newegg   Prices include shipping, taxes, rebates, and discounts     Total (before mail-in rebates) $1069.92   Mail-in rebates -$55.00   Total $1014.92   Generated by PCPartPicker 2019-04-15 19:29 EDT-0400    
So the 9400F is going to beat out the 2600x (even when it's OCed) by a decent margin in almost all games (see below for data) for a lower price. The 2060 should be perfect for maxing out most games (but not all) at 1080p60. The theme is black and white like you asked for (pictures below). 1TB of SSD storage should be great, and the build is just sexy  

 

Check out this build: 
PCPartPicker part list / Price breakdown by merchant Type Item Price CPU AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor $164.89 @ OutletPC CPU Cooler ARCTIC - Freezer 33 eSports Edition (Black/White) CPU Cooler $47.11 @ Newegg Business Motherboard MSI - B450 TOMAHAWK ATX AM4 Motherboard $114.99 @ B&H Memory Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory $94.99 @ Amazon Storage Samsung - 860 Evo 500 GB 2.5" Solid State Drive $77.99 @ Amazon Storage Western Digital - Caviar Blue 1 TB 3.5" 7200RPM Internal Hard Drive $44.89 @ OutletPC Video Card EVGA - GeForce RTX 2060 6 GB XC BLACK GAMING Video Card $349.99 @ Amazon Case Fractal Design - Focus G (Black) ATX Mid Tower Case $53.24 @ Amazon Power Supply Corsair - RMx (2018) 650 W 80+ Gold Certified Fully-Modular ATX Power Supply $89.99 @ Amazon   Prices include shipping, taxes, rebates, and discounts     Total $1038.08   Generated by PCPartPicker 2019-04-15 19:28 EDT-0400