RainStryke
No problem, thanks for the blue ribbon Cool GTX!
 
X299 is a great chipset. Here in 6 days we are expected to see the new i9 10th generation stuff from Intel, no idea if it's going to be on Amazon that soon though. The i9 10900X is looking pretty good. However, the i7 9800X has dropped down to 299 recently and that's an awesome deal if you have a Microcenter around... Might even be worth the drive, unless you need to spend more than $260 for gas and your time, who knows you might even enjoy it.


If you stay with the i9 9900K and return the X299 Dark, then I would look towards a Z390 board, anything with that chip set will fit the i9 9900K. If you go with the Z390 Dark from EVGA, then I would recommend going with some of this RAM:
https://www.newegg.com/patriot-16gb-288-pin-ddr4-sdram/p/N82E16820225144?Description=patriot&cm_re=patriot-_-20-225-144-_-Product

I originally purchased those and found out they were not compatible with anything I had. A guy here on the forums got his to 4800MHz on his Z390 Dark.
https://forums.evga.com/Patriot-viper-steel-ddr-4400-MHz-is-cheap-17000-ish-m2964431.aspx

Im not sure to return the unopened X299 to Amazon and see if they hit me with a restocking fee of 15%.  Gonna mark calendar to see i9 10th gen chip to see what socket it requires.  It makes no sense to but a 400-500 motherboard and go with an old CPU.  Im not sure.
 
In the meantime research a Z390 DARK motherboard. EVGA Z390 DARK, 131-CS-E399-KR, LGA 1151, Intel Z390, SATA 6Gb/s, USB 3.1, M.2, U.2, EATX, Intel Motherboard
 
Give me time to buy these daily deal items like EVGA PowerLink, Support ALL NVIDIA Founders Edition & ALL EVGA GeForce RTX 2080 Ti/2080/2070*/2060*/SUPER*/GTX 1660 Ti*/1660*/1650/1080 Ti/1080/1070 Ti/1070/1060  for $10 bucks delivered.
 
Bummed out to miss an 1000w Power supply for $140.
 
 

Sgt Hoit
Not sure if you're into buying used parts, but here is one the won't be there long:
https://www.heatware.com/for-sale/EVGA-X299-DARK-mobo-Intel-9800x-CPU-cpu-memory-motherboards-3434.html
I just bought something very similar on these very forums.

I don't want to be penny wise and pound foolish.  The cost of my time especially free time is IMHO high since work 6 days a week.
New you can get the x99 DArk for $439 Amazon and the i7 for $300 Egghead.  

RainStryke
If that box is unopened, you should be good to return the X299 Dark for an exchange, maybe they won't hit you with a restocking fee. If this rig is primarily for gaming, your best bet is to stick with the i9 9900K and get a Z390 motherboard, it has to be Z390 to work with the i9 9900K.
 
Any one of these Z390 boards would work just fine:
https://www.newegg.com/p/N82E16813188197
https://www.newegg.com/p/N82E16813119188
https://www.newegg.com/p/N82E16813145091

Back in the day ya picked motherboards that "worked" having the least bugs with peripheral components.
 
How do you know which is a better motherboard?  I figure a EVGA motherboard matched to a EVGA GPU  because all the quirks to a complex system ARE NEVER explained to the consumer. Most likely there are probably some hardware / software enhancement to same brands married to each other. I know they all have NVIDIA chipsets but I'll bet some engineer put a little "extra" for mating EVGA GPU to EVGA CPU.  Again went to a couple "best motherboards for 2019" and no detailed analysis. Just testimonials.
 
I just bought a Pioneer "radio"  AVIC-W8500NEX and requires a 64GB USB to be moved back and forth multiple times between the unit and an internet source.  To make it more complex the physical hardware is a 3rd party vendor AXXIS , then Pioneer for basic operations and another 3rd party based in Hungary (only email) to get the GPS / mapping  unit up to date. Then Sirius XM , Car space harmonic calibration etc.   Trying tio figure out how to get up to date traffic, and resoluteion to all the cameras plus have them record to a micro SD card.
 
For this build ; picking a power supply rationale and priority is length of warranty first , then watts and wiring.
 
So of these 3 motherboards which work best?  With my above comments all be equal Im getting EVGA because of EVGA GPU.