So I can tell you, 4 sticks is a crapshoot on any motherboard, it's not just with this one - it's actually highly recommended you don't run 4 sticks by most people that do RAM overclocking/board analysis, I.E. Buildzoid/Actually Hardcore Overclocking has said in more than one video "Yes, your motherboard has 4 RAM slots. That's a design flaw, not a feature" - meaning it's not actually intended to be used in any real fashion. I'm surprised you can even make it in to Windows from just leaving everything on Auto in BIOS, I had to change a lot of settings to get Windows stable enough to even use when I was testing 4 sticks.
I can tell you from my experience mixing kits, and yes it's considered mixing kits even if you use 2 of the "same" kit, because it's not a native 4x?? kit, on AM5 specifically, it either won't work at all, won't be stable, or the highest speed you'll be able to run stable is around 4800-5200MHz. I tried this with my current 2x48GB kit & the 2x16GB kit I had previously (I needed more RAM for rendering stuff, which is why I got the 96GB kit), on my old motherboard, and I couldn't get it to even BOOT/Train above 4400MHz - which at that point, you're better off just running one kit.
My suggestion would be run the 2x32GB kit, unless you actually NEED more than 64GB of RAM, like I did, in which case it's time to get you a 2x48GB kit like I did - they ain't cheap, but it's really nice to have all that RAM available in 2 sticks. I got a kit that's on the QVL for the X870E-E Strix (not that the QVL means jacks**t these days), and while it won't run at 6400MHz because my CPU doesn't like running the memory controller that high (at least I think that's the issue), I can run it at 6200MHz CL28 (which faster in terms of latency and overall performance than the EXPO speed on this kit of 6400MHz CL32) with pretty tight timings, but that's a 1.5v VDD, which I don't recommend unless you have a fan blowing on your RAM area, as it's likely settings like what I'm running would lose stability if the sticks get over 50-55C.
If you want to take a gander, there's a non-Royal version of the kit as well for slightly cheaper, https://www.amazon.com/gp/product/B0D7QZ7NWF/ it's also available on newegg for about the same price.
