PopsicleHustler

I would go higher to RX580 or 590 if possible.

It all depends on cost parts and expierence. You have to understand that things might go wrong at any moment, that's how life works. Pre-built might as Well go up in flames and you would get the blame for that. You never know.
 
I'm currently in a battle with eBay seller trying to refund 2 monitors with combined cost of 2500 euros because both have defects. But seller refuses to accept them saying that 'we do not accept returns, even though they must accept return if item is faulty. So I'm stuck with gaming PC with no monitor and 2 expensive at broken monitors. This year only I burned my CPU, and then 6 months later my GPU died. Life is hard, but I keep going.

Monitor CPU and GPU usage then. If you see GPU usage drops while CPU is at 100%, then it's most likely a CPU bottleneck. 

Plug one fan into CPU_FAN and set low fan curve in Bios?

https://www.amazon.co.uk/Corsair-CC-9011070-WW-MicroATX-Mini-ITX-Case-Black/dp/B00LA6WXEO/ref=sr_1_19?s=computers&ie=UTF8&qid=1543778864&sr=1-19&keywords=corsair+case

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

Flip the switch on the PSU, solved.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

Finally an RTX card that can handle DXR with over 60FPS on 1080p.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

9600k is 240GBP, 8700K is 420GBP with too little gain in gaming performance. And  I'm building gaming PC for online FPS games.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

I swear, there is an AMD employee working undercover at Intel with a mission to destroy Intel.

I would go with 3000Mhz RAM for Ryzen. Also, R5 2600 for 144Hz 1440p is iffy. I would go with i5 8600k/9600k if I could.