Originally posted by Adam However, note that the number of frames you get in practice really depends on the detail in the scene.
Plus the 4.4 fps and FF 17 RAW buffer specs in the manual are based on ISO 100 images. (Probably shooting a plain gray wall, or a simple black-and-white test chart). Hence smaller images, faster buffer clearance.
In Nikon, there are options for using 12/14 bit lossless-compressed RAW, as well as compressed 12/14 bit RAW. 12 bit RAW can shrink files and boost the amount stored in the RAW buffer by ~20-50% in cameras like the D800 or D810. If buffer boosting was a goal, that's probably the sort of RAW option Pentax engineers could implement in firmware quite easily.