Reddit mentions of Intel Optane SSD 900P Series (480GB, AIC PCIe x4, 3D XPoint)

Eh, You don't really want an i9, Kerbal is still single threaded, so you're primarily going to be affected by IPC and clock speed. An i9 is going to suffer in both, so you're spending more money for less performance.

You don't even really need to break the bank tbh, since you're not going to need a super high-end video card, and you don't need all of those extra cores or a shitload of memory.

If we take the consideration of a "Kerbal machine" seriously, your best bet would be to buy a 5.3Ghz 8600K from Silicon Lottery: https://siliconlottery.com/collections/all/products/8600k53g and put it in something like this: https://pcpartpicker.com/list/Wkvmkd I've spent a good chunk on the SSD and RAM here, since access times do have a measurable impact on most single threaded applications, but you could make either substantially cheaper and still get 95% of the way there. I've also spent probably more than necessary on the video card, since I'm not sure how much Kerbal relies on storing assets in video memory. My guess would be not a lot in vanilla, but this ought to help you with those sick visual mods you want :)

EDIT: I've done more research!

High-end KSP machine: https://pcpartpicker.com/user/Intercold/saved/gqzQVn

• It turns out KSP does benefit from hyper-threading, but only slightly (margin of error basically): https://forum.kerbalspaceprogram.com/index.php?/topic/34179-advanced-users-improve-ksp-performance-on-intel-cpus-with-hyperthreading-tested/
  
  
• I'm also not certain if more cache will help KSP (couldn't find any info anywhere), I know it does for other single threaded math-heavy games (such as Dwarf Fortress), so I'm going to go with an 8700K for a "Win-the lottery" style build. https://siliconlottery.com/collections/coffeelake/products/8700k52g?variant=47048295116
  
  
• I've also swapped the cooler for one of those recommended on Silicon Lottery's suggestions, and I've swapped to one of their recommended motherboards.
  
  
• I've increased the capacity on the SSD, since the 1TB model is slightly faster http://ssd.userbenchmark.com/SpeedTest/413203/PM981-NVMe-Samsung-1024GB. EDIT2*: This should perform substantially better, but it's not on Pcpartpicker yet, it will also eat one of your PCIe slots: https://www.amazon.com/Intel-Optane-900P-280GB-XPoint/dp/B0772T4BVZ?th=1
  
  
• I found slightly faster RAM as well (going by the handy CAS/Speed rule for access times). Note: using 2 sticks of RAM gives to redundancy, which is nice. You're also getting a slight speed boost if your MB supports Dual channel (most do).
  
  
• I swapped the PSU for something more reliable (Important for high OC) based on the list here: https://www.tomshardware.com/reviews/best-psus,4229.html
  
  
• Video card performance doesn't seem to matter at all from the research I've done, so I just chose a decent mid/low range card. Freesync also has some advantages over G-SYNC in my opinion (Controversial, but I like that it's an open standard, and it performs better at low FPS), so if you have a monitor that can support it, that's a plus.
  
  
• For this high-end build, if you wanted to go custom-loop, you might want to swap the motherboard for a Gigabyte Gaming G7. You don't want to go with that if you're not using a custom-loop though, since their VRM cooling is inadequate: http://www.overclock.net/forum/6-intel-motherboards/1638955-z370-z390-vrm-discussion-thread-5.html#post26380035
  
  
• And of course, for maximum cooling performance there's always the new Ncore direct die cooler coming out later this year: https://www.kickstarter.com/projects/341758082/ncore-v1-naked-die-cooling-waterblock-designed-by/
  
  For reasonable/budget minded people this should be more suitable: https://pcpartpicker.com/user/Intercold/saved/Ppwd6h
  
  
• i5 instead of i7, since as I mentioned, the performance difference is close to margin of error. Although you could still go for the fancy Silicon Lottery chips, for this price range you're not getting much more than the delid as far as clocks go, since 66% can reach 5.1: https://siliconlottery.com/collections/all/products/8600k51g
  
  
• Cheaper PSU, since you'll be getting lower clocks (probably), and thus pulling less wattage.
  
  
• Cheaper MB for the same reason
  
  
• More reasonable RAM (performance difference is probably too small to notice)
  
  
• More reasonable SSD (you'll maybe just barely notice)
  
  
• Cheaper case as well, since again, airflow isn't as important if you're not pushing those higher clock speeds.
  
  
• Cheaper AIO cooler for the same reasons. The H75 is well rated, and I can personally confirm that mine at least performs well even with a high OC hotwell (1st gen Haswell) processor, and it's quiet as hell.
  
  EDIT3: Typos, cleaned up a bit, added perma links for the second two builds since the high-end one somehow ended up with a not-up-to-date link.

PTU runs perfect for me, friend. Did you try installing to an Optane SSD? It seems to really help.