I made a custom imatrix dataset by slapping together random columns from some popular datasets on huggingface and formatting using the official jinja template. Comapred to the unstructured bartowski dataset, PPL went from multiple thousands to single digits, so I think it should be good now.
Just in case, I mirrored the old static quant to https://huggingface.co/Beinsezii/gemma-4-26B-A4B-it-GGUF-6.52BPW-static
Fits ~75k F16 CTX + MMPROJ on a 24GiB GPU, or ~150k CTX without vision. Measured on a DE, not headless.