Stuttering playback in PPro with GH5 10 bit files

[JustinWoo]

Any help folks could render would be greatly appreciated. Here's my problem:

1. I get a ton of playback stuttering when playing back 10 bit GH5 VLOG files (GOP, H.264 codec, I think) in my sequence. It makes editing very slow and difficult.
2. The sequence window says "MEDIA PENDING" for quite a while after I open a project. Up to ~3-5 minutes sometimes. I basically have to go get a cup of coffee before I can edit.
3. I also get delays when I hit play, especially when I first open a project. Sometimes these delays are VERY long and sometimes they're only a few seconds long. They're much longer when I first open a project.

My system specs: i7-8700K (not overclocked) 16 GB RAM running at 3200 (I made sure of this via enabling the XMP profile in BIOS) GTX 1080 Ti (latest drivers as of last month - I heard the last drivers were buggy so I'm waiting for that to get sorted before I update) ASRock Fatal1ty K6 X370 Mobo OS is on M.2 Intel SSD (NOT NVME) Footage on a Samsung 860 EVO SSD connected via SATA. Dell Ultrasharp 4K monitor as main monitor, crappy old Insignia 1080p monitor as a side monitor.Here's what I've tried to fix this problem:

1. Performed a clean install of the GPU driver.
2. Updated all relevant mobo drivers, chipset drivers, and BIOS.
3. Moved all footage and project files to a Samsung 860 EVO SSD. I also use this drive for scratch and media cache. It's 1TB and it's about 1/3 full.
4. Reset Premiere's preferences by holding Alt when I booted the program.
5. Set playback to 1/2 and 1/4 quality (no change)
6. Activated High Quality Playback.
7. Deactivated High Quality Playback.
8. Disabled GPU usage on Mercury Playback Engine. Made the problem way worse. (When enabled, it uses about 13-20% of the GPU, according to my task manager)
9. Uninstalled / Reinstalled Premiere Pro
10. Run PPro as an Administrator.

I haven't tried proxies yet, and while I'm betting this would solve the problem (even my 4 year old laptop was able to edit this footage when I proxied it), I'd rather not if I can at all avoid it. I hate the speed bump that proxying adds to my workflow, and I got this new computer in order to avoid having to do that.

As far as I can tell, it's not a disk access error. My Samsung SSD uses less than 20% of its throughput even when playback stutters badly.

The CPU occasionally spikes to 100%, especially when a new clip is coming up in the sequence. I've heard stories about people using this footage fine with the same specs as me (some of them were overclocked up to 5.0 Ghz though, and I wonder if I should pursue that. I'll need a really good cooler though, because even mild OCing causes this chip to get real hot. I currently have a pretty simple Cooler Master air cooler and would probably need an AIO water cooler or something).

RAM usage often spikes to 13 (out of 16) GB when I'm playing back a sequence.

I'm also considering re-installing Windows though I'd REALLY rather not if I don't have to.

Things I'm doing that may affect things but may not: I'm using an external sound interface for all sound playback. (Scarlett 18i6) This 4k footage is scaled down to a 1080P timeline. I have 5 channels of video, but the project itself is about 2 minutes and pretty simple. Most of the channels beyond the first two are simple b-roll clips.

Any help or advice would be greatly appreciated.

[Jim_Simon]

I do recommend using Cineform proxies for all H.264 media, regardless of machine specs.

[JustinWoo]

I'm hoping to avoid having to use proxies, and I've spoken to other folks with my same specs that are able to avoid it. I'm hoping to do the same.

[Jim_Simon]

My advice then would be to give up hope.

Use the proxies.

[JustinWoo]

Didn't give up hope. Formatted drive and reinstalled a clean copy of Windows 10. Works MUCH better now. I still stutter, but it's VERY occasional, as opposed to constant.