Question i7-9700k > 128GB?

Dec 25, 2016
The i7-9700k officially supports 128GB of RAM but Linux reports a 39 bit physical address but which is enough address space to address 512GB (2^39 = 512GB).
At the time the CPU was released, the largest DDR4 DIMM available was 32GB, and given that the CPU has only two memory channels and that placing more than two DIMMS on a channel would result in more capacitance than the address lines can drive, 128GB was the practical limit.
But now Corsair has released a reduced load 64GB DDR4 DIMM, and I'm wondering if 4 of these could be used to achieve 256GB of RAM? Possible limiting factors I can see are, 1) The motherboard may not actually wire all 39 address lines since none of the CPUs it supports address more than 128GB. 2) Even reduced load DDR64GB might be too much capacitance for the CPU to drive. 3) There may be other limitations of the Z390 chipset that I am not aware of.
I presently have this machine clocked at 5Ghz all cores and with aid of a robust cooler have it running in an acceptable temperature range. But would like more RAM. I'm not an AMD fan, don't want to start a religious war over AMD vs Intel but I've got my reasons and am looking for a solution that can address more memory at this speed. Intels Xeon chips seem to not clock as well.