I’ve calculated the exact crop factors for each aspect ratio on the GH5s based on camera specs:
3680 pixel long in 4/3 = 2x crop factor in 4/3 still mode
3840 pixel long in 3/2 = 1,91x crop factor in 3/2 still mode
4016 pixel long in 16/9 = 1,832x crop factor in 16/9 still mode
4096 pixel long in 17/9 = 1.796x crop factor in 17/9 (DCI 4K) video mode
3840 pixel long in 3/2 = 1,91x crop factor in 16/9 4K UHD video mode.
35mm means 3680×3680 = 7360 pixel long or 1x crop factor
If you add a Speed Booster Ultra to the GH5s you get in DCI 4K a crop factor of 1,275x with 35mm lenses.
If you add a Speed Booster XL to the GH5s you get in DCI 4K a crop factor of 1,149x with 35mm lenses.