Stuttering when adding Transitions / Multiple Videos / FX

Hi Folks,

I am having a couple of problems with Davinci Resolve and I keep forgetting to post about it - I've remembered now whilst at work so I figured I would just get the post done and can post my logs and the like later.

Problems

I seem to get a problem when multiple videos are loaded, it can sometimes get really jerky/stuttery - especially as I often use the delta keyer to remove the background.

When I start adding in transitions or other effects it becomes much worse.
Some transitions won't even play properly when they are the only effect on - they just stutter and jerk and jump round the video.

the stuttering and jerkyness usually affects both the audio and video, but is sometimes just the video - things will "keep playing" in edit mode but you'll just see that you've missed about 10 seconds of video.

Also, whilst working on a video it can get progressively more unstable as things go on, occasionally Davincii will just close without warning (most of the time it is saved up to the last moment though)
Closing and opening the program can, at times, improve performance slightly.

Programs stored on an M2 drive
Most data(except images) stored on SSD - so shouldn't be the drives causing this.

I tend to record from SLOBS (Streamlabs OBS) and have changed the recording settings to use x264 software encoder instead of the NVIDIA encoder (Nvec) - this has resolved the issues where files where showing up as media offline after import.
Most Video is recorded in 1440p 60FPS
Most Video is Produced in 1440p 60FPS

I've read through a number of different tutorials and options on what to do about Optimized Media, Proxy Media, Fusion Cache and all that.
Sometimes when I generated Optimized Media it all goes offline when I load the project back up.
Sometimes the Optimized and/or Proxy media seem to make things slower rather than quicker.

I've noticed the program doesn't like when I have all in one messenger open, so am sure not to have that open ever, but not noticed any other issues with other software.

I think at least one of these must be true
- I have got something wrong in my settings (likely)
- I am doing the optimised and/or proxy media wrong (less likely but still likely)
- There is a general issue with the program (doubt it as others don't have these issues, right?)
- My System isn't good enough for the settings (possible)
- Davinci doesn't like the x264 even if it prefers it over the NVEC and I am kinda stuck

Also - does anyone have any suggestions for system upgrades that would make this problem go away without not too much of a headache (and hopefully not buy a 4080 cos I do't have the money for that haha)

My System

----High Level----

CPU: AMD Ryzen 9 5900X
MOBO: SUS ROG Strix X570-F
RAM: Corsair Vengeance RGB PRO Black 32GB
GPU: MSI GeForce RTX 3070 Ti VENTUS 3X 8G OC
CASE: Corsair iCUE 5000X RGB
COOLING: Corsair iCUE H115i PRO XT RGB
PSU: Corsair RM850x 850W
AUDIO: Scarlet 4i4

STORAGE

Windows Drive - Samsung 980 PRO M.2 NVMe
Programs Drive - WD_BLUE SN550 1TB M.2
Fast Storage Drive - Samsung 870 QVO 2 TB
Other Store - Western Digital Blue WD40EZAZ 4TB SATA

OS: Win 10 Pro


----Detail/Links----

CPU: AMD Ryzen 9 5900X (12C/24T, 70MB Cache, up to 4.8 GHz Max Boost)
https://amzn.to/3X8KZg0

MOBO: ASUS ROG Strix X570-F Gaming ATX Motherboard, AMD Socket AM4, Ryzen 3000, 14 Power Stages, PCIe 4.0, M.2, DDR4, Intel LAN, HDMI, DP, USB 3.2, Aura Syn
https://amzn.to/3X9yosH

RAM: Corsair Vengeance RGB PRO Black 32GB 3200MHz DDR4 Memory Kit - https://www.scan.co.uk/products/32gb-2x ... xmp-20-135
Equivalent amazon link - https://amzn.to/3JJfpSZ

GPU: MSI GeForce RTX 3070 Ti VENTUS 3X 8G OC Gaming Graphics Card - 8GB GDDR6X, 1800 MHz, PCI Express Gen 4, 256-bit, 3x DP v 1.4a, HDMI 2.1 (Supports 4K) https://amzn.to/3JJfpSZ

CASE: Corsair iCUE 5000X RGB Tempered Glass Mid-Tower ATX Smart Case (Four Tempered Glass Panels, Corsair RapidRoute Cable Management System, Three Included https://amzn.to/3JNoDNZ

COOLING: Corsair iCUE H115i PRO XT RGB Liquid CPU Cooler (280mm Radiator, Two 140mm Corsair ML Series PWM Fans, 400 to 2,000 RPM, Advanced RGB Lighting and Fan Control with Software, Easy to Install) Black https://amzn.to/3DO7X5c
PSU: Corsair RM850x 850W Modular 80+ Gold PSU - https://amzn.to/3XbCMYp
AUDIO: Scarlet 4i4 - https://amzn.to/3YtzjFt

Storage

Windows Drive - Samsung 980 PRO M.2 NVMe SSD (MZ-V8P500BW), 500 GB, PCIe 4.0, 6,900MB/s Read, 5,000MB/s Write, Internal Solid State Drive - https://amzn.to/3YhqE9K
Programs Drive - WD_BLUE SN550 1TB M.2 2280 PCIe Gen3 NVMe up to 2400 MB/s read speed - https://amzn.to/3l6q3su
Fast Storage Drive - Samsung 870 QVO 2 TB - https://amzn.to/3JR1IRQ
Other Store - Western Digital Blue WD40EZAZ 4TB SATA 6Gb/s 3.5" Hard Drive WD Blue - https://amzn.to/3jDrFd2