Suspect3d

Ya I was thinking it would be good, the pro version when I pick this up for like 3 weeks out so I ordered this one instead. it's a great cooler I wasn't sure I needed to swap over to an AIO for the 5900x. I mean i'll just use it and see what happens. easy thing to fix.

You should be fine the cooler you have is really good but if you want extra assurance get the pro version of the dark rock 4 pro air cooler but the one you have right now will do the job just fine so its really not needed but the option is there

Nh d15
Dark rock pro 4
Assassin 3
Silver Arrow IB-E Extreme Rev. B 
Le GRAND MACHO RT
PH-TC14PE
 
Are all beefy killer coolers that can handle your cpu just find.

https://pcpartpicker.com/product/84MTwP/noctua-nh-d15-chromaxblack-8252-cfm-cpu-cooler-nh-d15-chromaxblack (looks to be unavailable at the minute)
https://pcpartpicker.com/product/R6kgXL/noctua-nh-d15s-chromaxblack-8251-cfm-cpu-cooler-nh-d15s-chromaxblack
https://pcpartpicker.com/product/F3gzK8/be-quiet-dark-rock-pro-4-505-cfm-cpu-cooler-bk022
https://pcpartpicker.com/product/ZLtQzy/noctua-nh-u12a-6009-cfm-cpu-cooler-nh-u12a

The Noctua NH-D15 is quite good

I live in New Zealand so all those prices are in NZD btw

What cooler did you get? I got a NZXT X52 and it's crap. I'm at 80C max in aida64 with 1.337V and that's 51C over ambient. 

I don't actually have that cpu or that motherboard so I really can't help you on how it all works and what the options are. They are all different for some stupid reason. I think bios settings and naming should be standardized, just a pet peeve on mine.
 
I would only reiterate that you should test it on things you actually do on your computer and not rely solely on benchmark results, or even bother with them honestly. It either works better for your use case or it doesn't, that is the bottom line. There is no point in putting extra stress and heat on your parts if it gives you little to no gain with what you intend to use it for. If I overclock my cpu, memory and video card (which I did) yes my benchmark scores go up. R15 showed a slight improvement and gaming benchmarks like time spy and fire strike went up as well. So did my voltage, wattage and heat output. However when I fired up a couple of games that I actually play it made no difference at all. Like Project Cars 2, it made no difference at all. I run this game at 4k on a 60 hz 55 inch tv. Most of my setting are ultra, except the effects I don't like and I turn those off. I use Vsync that locks my fps 60 fps because I hate screen tear. My video card only uses between 1200-1400 mhz while playing and it never comes close to dipping below 60fps, even before I overclocked everything. So for me overclocking makes zero sense. Now if I get a new game or something and it has trouble holding 60fps then yes overclocking might be an advantage. Or I could just tweak a few settings in the game possibly.
 
 

CPU cooler clearance is usually listed in case specs and that can be compared to the cooler's height. Cooler specs may also include RAM clearance and that can be compared to the RAM height but you may have to resort to reviews for reference.
Depending on how much you prefer to spend, good options include:
Gammaxx 400: https://pcpartpicker.com/product/hJFPxr/deepcool-cpu-cooler-gammaxx400
Macho Rev. B: https://pcpartpicker.com/product/4TCrxr/thermalright-cpu-cooler-machorevb

4.2ghz is the boost clock which is not pbo and i think its only on a few cores not all the cores

My Dell U2515H?
No Freesync or GSync. I do have it overclocked to 80Hz.
 
Works great, I haven't had any issues with it aside from the power button (capacitive, not a physical button) being a bit iffy, but I let it go to sleep instead of turning it off, so that's not a big deal. I'd buy a second one if Dell was still making them, but sadly they've been discontinued and replaced by the U2518DX which seems to be more issue prone. Hard to find the U2515H for a reasonable price now. I had paid about $300-330 for mine if I remember correctly.