Need help stabilizing 64GB RAM (2×32) at 6400/28 on 9950x/x670e Taichi

Big noob here trying to stabilize my RAM before my return window closes. My goal is to achieve 6400/28, which I realize might be tough.

Timings/specs here

Current Setup:

• AMD 9950x with Phantom Spirit 120 EVO
• Asrock x670e Taichi
• RTX 4080 Super 16GB
• NZXT C1200 ATX 3.1 PSU
• Kingston Fury kit (2x32GB, 6400 CL32, Hynix A-die) – on QVL

Progress So Far:

• Managed to boot at 6400/28
• Increased VDD and VDDQ to 1.6v for better stability

Current Issues:

• IRQL BSOD during memory tests
• Errors in benchmarks (7zip, y-cruncher, y-prime)
• 0 CPU score in Timespy Extreme
• DPC Watchdog BSOD

Questions:

1. Any suggestions on timings/voltages to change to stabilize things?
2. Why might my CPU perform above average in single-core tests but below average in multi-core tests?

I also have a KLEVV kit (2x32GB, 6400 CL32, 1.35V, A-die) as an alternative option if we think my Kingston kit is to blame. I would probably prefer to keep the KLEVV kit as it was ~$55 less than the Kingston, but first I'd like to stabilize the Kingston if possible.

Let me know if there are any other screenshots that would be helpful.

Thanks in advance!