I just picked up a GSkill F4-3600C16D-32GTZN kit and I’m having trouble running both XMP and manual settings on an EVGA Z390 FTW with a 9900k.
I’m not able to boot the rated 3600mhz 16-16-16-36 1.35v. However, I can boot if I lower the clock 100mhz down to 3500.
I’ve tried booting at 1.4 and 1.45v and also setting VVCIO and VSA to 1.2-1.25.
 
Did I get a bad kit or is it more likely my motherboard or my 9900k’s memory controller simply aren’t capable of this speed?
3500mhz has been stable for quite a few loops of Cinebench and a few hours of gaming but I’d really like to achieve that last 100mhz. Or even better; push to 4000mhz with slightly looser timings. Is it common for the 9900k's IMC to handle speeds around 4000mhz?

You basically have the same RAM as I do, slightly different model #, but it's CL16, 3600MHz, 1.35V.  Is yours also Samsung B-Die?  If so it's very odd the board won't work with it.  
Is the RAM listed on the motherboard's QVL?  If not, it's probably secondary timings that the eVGA BIOS is configuring incorrectly and causing the boot issues.
As an experiment, try inputting as many of these as you can manually, and see if it boots:
 

 
The RTL/IO-L/tRDRD/tRDWRetc timings you shouldn't have to worry about, but I would try to do as many of the others as you can, in particular tWR, tRFC, TRRD_L, TRRD_S, tRTP, tFAW, and tREFI - those are pretty important and may be set wrong by a BIOS that doesn't know what your sticks are.
 
Also, is your kit 4x8GB of 2x16GB?  As far as I know, eVGA Z390 motherboards are Daisy-Chain (I'd have to look it up to be sure though), which means they prefer 2 stick kits as opposed to 4 DIMM kits.
 
Hope this helps.