Any suggestions to further tighten my memory overclock? (3400@15-16-16-32) (8x16gb ddr4 on x299/skylake-x)

Looking for any suggestions / obvious areas for improvement on my memory overclock.

HERE is an imgur album showing the full set of RAM timings + voltages in the UEFI.

Im running 128gb (8x16gb) ddr4 in quad channel mode on intel's x299 platform. CPU is a skylake-x i9-7940x.

The ram sticks are gskill / samsung b-die and were sold as 3467@16-18-18-38. They are duak rank sticks. Currently running them at 3400@15-16-16-32 with tightened secondary timings but automatic tertiary timings and RTLs / IOLs.

Motherboard is an asrock x299 i9 professional gaming

The hardware is all a bit on the older side but is still extremely capable.

A few notes:

1. Increasing VCCIO / VCCSA / DRAM voltages seems to hurt stability, not help it. This is strictly a guess, but I think the skylake-x IMC is probably working overtime and cant handle the additional heat that increasing voltages bring
2. manually setting RTL's or IOLs seemingly prevents the system from booting 100% of the time. This includes the case where I set them to the automatically determined values.
3. There are a bunch of options for NOM / PARK / WR that I am completely clueless about, so ive left those all on auto.
4. 3400 MT seems to be the "sweet spot" for frequency. If I increase to 3600 I have to drop main latencieds to something like 3600@20-24-24-40, and even that I dont think was fully stable. If i drop frequency to 3200 I can get 3200@14-16-16-32 with around the same secondary timings, and 3400@15-16-16-32 seems like it is all around better.
5. The system runs linux ((fedora 40), not windows. Im happy to run tests/benchmarks on request, but they need to have linux versions for that to be possible.