maximum project sizes when working in 4K in adobe premiere pro

Hello, It sounds like you're encountering memory management issues while editing 4K video files in Adobe Premiere Pro, despite having a reasonably powerful editing PC. Here are some suggestions to help mitigate the problem:

Proxy Workflow: Making proxies is indeed a great solution to reduce the workload on your system. Premiere Pro allows you to create lower-resolution proxy files that are easier to edit, while maintaining the option to switch back to the original high-resolution files for final export. This can significantly improve performance, especially when working with large 4K files.
Import Media: Start by importing your high-resolution 4K video files into your Premiere Pro project.
Select Media: In the Project panel, select the media files you want to create proxies for. You can select multiple files by holding down the Ctrl (Windows) or Command (Mac) key while clicking on each file.
Right-Click and Choose Proxy: Once your media files are selected, right-click on one of them and choose "Proxy" from the context menu.
Create Proxies: In the submenu that appears, select "Create Proxies..." This will open the "Create Proxies" window.
Choose Proxy Format: In the "Create Proxies" window, choose the format and resolution for your proxies. Premiere Pro offers several preset options, including low resolution (e.g., 480p or 720p) and different codecs (e.g., ProRes, H.264). You can also create custom presets if needed.
Location: Specify the location where you want Premiere Pro to save the proxy files.
Start Ingest: Click on the "Ingest" button to start creating proxies for the selected media files. Premiere Pro will begin transcoding your high-resolution files into the specified proxy format.
Monitor Progress: You can monitor the progress of the proxy creation process in the "Background Tasks" panel. Depending on the number and size of your files, this process may take some time.
Switch to Proxy View: Once the proxies have been created, you can switch to proxy view in Premiere Pro by clicking on the wrench icon in the Program Monitor and selecting "Toggle Proxies."
Editing with Proxies: With proxy view enabled, you can now edit your project using the lower-resolution proxy files. Editing with proxies should result in smoother playback and improved performance, especially when working with large 4K files.
Toggle Back to Original: When you're ready to export your final project, you can toggle back to the original high-resolution files by clicking on the wrench icon in the Program Monitor and selecting "Toggle Proxies" again. Premiere Pro will automatically use the original files for export.

Also you can do the following:
Avoid using Long-GOP (Group of Pictures) media formats, particularly when dealing with 4K footage. Long-GOP codecs, such as H.264, are highly compressed and can be particularly taxing on system resources, especially when decoding during editing. This compression can lead to increased processing demands and decreased performance, particularly with high-resolution 4K content. Instead, opt for intra-frame codecs like ProRes or DNxHR for your original 4K footage. These codecs maintain each frame as a standalone image, making them easier to edit and work with, especially when using proxies. If your original 4K footage is already in a Long-GOP format, consider transcoding it to an intra-frame codec.
Optimize Project Settings: Review your project settings in Premiere Pro to ensure they are optimized for your system. This includes adjusting playback resolution, render settings, and other preferences to reduce the strain on your computer's resources.
Memory Allocation: Premiere Pro allows you to adjust the amount of RAM allocated to the program. You can try increasing this allocation to see if it improves performance. Go to Edit > Preferences > Memory, and adjust the "RAM reserved for other applications" slider.
Close Background Applications: Close any unnecessary applications running in the background to free up system resources for Premiere Pro. This can help prevent memory contention and improve overall performance
"GPU/CPU/RAM Tweaking apps in particular".
Update Premiere Pro: Make sure you are using the latest version of Premiere Pro. Adobe frequently releases updates that include performance improvements and bug fixes, which may help address memory management issues.
Check Hardware Compatibility: Ensure that all your hardware components, including CPU, GPU, and RAM, are compatible and properly configured for optimal performance with Premiere Pro.
Monitor Resource Usage: Use system monitoring tools to keep an eye on your computer's resource usage while editing. This can help identify any bottlenecks or issues that may be affecting performance.

It depends on the specific media in use, the specific effects used, and the specific GPU. Without that, "we" are just making wild guesses.

In general ... long-GOP media is more likely to have issues because you aren't simply playing back individual frames. The computer has to recreate and store up to 40-100 frames before it can even begin playback, depending on what device created it. DJI drones are often using partial iframes, so at times their clips go over 100 frames between complete iframes. 

And some of the say A7 type long-GOP that is 422/10 bit and fairly high bitrate is also a slog for the system to process. Some of that can't be 'hardware decoded' by any hardware, so that really stresses your system.

AVCHD is also mostly long-GOP, and can be a pain in the tush.

But without knowing your specific gear/media/effects, no particular help is available.

And 6 cores, only 32GB of RAM ... should be ok for 1920x1080, in ProRes ... but if you're doing much to it, or there's long-GOP clips, that's a bit light for 4k and up. Especially if your GPU is under say 10GB of vRAM.