So after a few hours playing around with A1ex's second release of the 1.1.3 firmware, here's what I'm getting with 14bit lossless option:
3520 x 1320 = max. 1314 frames - ISO within 200-400 range - scales up to UHD with no perceived loss of quality
4096 x 1862 = max. 507 frames @ 12.5 fps - Not sure how useful this would be for landscape work or slow shots. Again ISO within 200-400 range.
Previews: At the moment, not fantastic but definitely better than a black screen. I was able to rack focus with a moderate degree of success.
Camera crashes persistently when using 50/60p