I didn't build it for KSP (even a low end/very old PC can probably run this reasonably well), rather for much more intensive games, but I've got the following:
-AMD FX-8350 processor (I don't bother with overclocking, never needed to)
-32gb of RAM (overkill, I know)
-NVIDIA GeForce GTX 960 (I plan on upgrading this later this year or next)
-I have two 256gb SSD's. I was originally just going to have one SSD and then grab something bigger for mass storage but was sent a second one for some reason, so... *shrug* Free stuff. 500'ish GB of storage is a bit less than I'm used to but I only ever have a few games installed, so it's manageable. I keep most of my games on the second SSD.
-Windows 10 64 bit
It works well. I get 60fps (or near enough) with everything I throw at it, only dropping a bit in certain instances and even then it's barely noticeable. I'll probably upgrade the graphics card some other time and grab a rift once there are more games out (like Star Citizen, hopefully) to make it more worthwhile.