Depending on the source, your debayer readings could well be CPU bound. We tested and found the new dual 14 core config is prefered for RED, Sony F65 etc images. Almost any modern GPU will be waiting for the single six core to decompress prior to the GPU debayer.
This is exactly the process used with the full version of Resolve and the PostGres shared database.You can even use a database server to manage all the projects. Details in the config guides and manual.
While there is some panel latency the fundamental problem is that The Q4000 is a good GUI card but not very powerful for image processing.
Consider adding one of the hi performance GPUs listed in our config guides, published on our web support site.
Are u rendering individual clips and with the same frame numbers overwriting each clip?
What happens when u render one clip as dpx? Same one as a tiff to a different folder?
What do u find?
It is possible that other LUT generation apps use the .dat or .cube file extension but the format within the file is not recognised by Resolve. Open the .cube that does not work with text edit and compare the structure to one that does.