[Help] Low Write Speeds with Hynix DJR – Need Advice on GDM, Timings & FCLK Stability (5800X + 2x16GB)

Hey everyone,

I’ve been tweaking my RAM setup (2x16GB G.Skill F4-3600C16D-16GTZNC – Hynix DJR) over the past couple of days and have managed to hit 3866 MT/s @ 1.55V (haven’t tried lowering it yet). It passes TM5 (1usmus config), a 1-hour OCCT run, and I even gamed on it (Last of Us II) for 4+ hours with zero crashes. Still pending long stress tests for full stability.

Main issue:
My write speed is really low compared to read and copy:

Read: ~55 GB/s

Copy: ~54 GB/s

Write: ~30 GB/s

I expected better write performance at these settings. Any idea what's causing this? What can I tweak to fix it?

Trying to stabilize with GearDown Mode OFF, but it's tricky. Runs fine with GDM ON.

Are there specific subtimings I should adjust to get GDM OFF stable?

Previous setup:
I had a 5600X (Hydra rated it Platinum) and ran 4000MHz CL16 @ 1:1 with 2000 FCLK, 1.050V IO, 1.125V SoC, 1.525V DRAM — fully stable on a similar Hynix DJR kit (2x8GB SR).

Current CPU: 5800X (not great IMC):

Flat-out refuses to boot at 1900 FCLK, no matter the voltage (bug maybe?)

1933 FCLK is stable at stock volts (but I’m running 1.125V SoC just in case)

I can boot up to 2066 FCLK with 1.15V SoC, but anything over 1933 throws WHEA errors

Even 1966 FCLK gives WHEA, despite trying 1.22V SoC + 1.125V IO

Only actual crash happens at 2066 MHz, rest just throw WHEA warnings

My questions:

1. Why is my write speed so low? How do I improve it?

2. Which subtimings should I adjust to help stabilize with GDM OFF?

3. Any tricks to eliminate WHEA errors above 1933 FCLK and push to 2000?

4. Is it worth trying lower DRAM voltage (currently 1.55V)?

Any help, suggestions, or experiences would be seriously appreciated. I’ve been deep in subtimings all week — literally dreaming in tRFC and tRAS values at this point!

Thanks in advance!