Although you might be controlling the lighting, you should get better low light performance at 6K since more area will gather (4096/6144=.667x23.1=15.4, 15.4/17=.906x9=8.15 x 15.4=125.5 SQ mm, 23.1x12.99=300 SQ mm /125.5=2.39) 239% more light, and you might be able to close down the aperture for a sharper image and greater depth of field.
What lenses will you be using? If you are concerned about media costs, I suspect that you might not be using expensive Super 35 cine lenses.
At 4KBRAW, you can use high quality Super 16 cine lenses that are available at bargain prices. The 15.4mm sensor crop is close enough to the Super 16 film gate of 12.522x7.417mm that it does not vignette midway through it's range. Since they were designed to be blown up to 35mm, the best of them are on a par with or better than the best of the 35mm film lenses. Due to the current slump in lens rentals, companies are selling off their seldom used lenses, making them available. Their rental prices are considerably lower as well. The Director I got my Cooke from had it available for $100 USD a day on Sharegrid before he sold it. Others charge less.
Using the Cooke Varokinetal 10.8-60mm T3 (a 1975 9-50mm modified by Optex to cover Super 16) on a PL mount modified BMPCC 6K at 4K DCI braw, there is no vignette at 28mm and above. This is a full frame equivalent fov of (36/(4096/6144x23.1) x28) 65-140mm. An 87% crop at 10.8mm removes the vignette, for a full frame equivalent fov of ((36/(4096/6144x23.1) x10.8)/.87) 29mm. There is no vignette at the 2.8K sensor area throughout the zoom range. The going price for this lens is less than 3% of it's original 1975 price.
EDIT: Until I do more research, I am not sure if Super 16 lenses are compatible with the BMPCC 6K if it has the factory EF mount or the Wooden Camera PL mount modification. Super 16 lenses are not listed on the compatibility list from Wooden Camera.
Although the Cooke Varokinetal 10.8-60mm T3 lens has a profusion from it's flange of 30mm, well below the 40mm maximum for a Wooden Camera PL mount, I am using a 2019 Bezamod "deep mod", that unlike their regular one, was advertised as being compatible with Super 16 lenses. On this camera the surface of the PL flange mount to the collar above the sensor is 37mm. The end of the camera body snout to the surface of PL flange mount is 12.5mm.
The previous owner of this lens used it with a Wooden Camera PL mount modified BMPCC. He had an issue with a lack of infinity focus near the widest setting. Happily, with the Bezamod "deep mod" modification, I can get infinity focus from 10.8 to 60mm on the Cooke 10.8-60mm lens on my BMPCC 6K.
I found this post from 2019:
Jean Capdouzey said:
"You will never get 16/S16mm C-Mount lens to reach infinity focus on the P6K, never....unless a piece of optics was inserted between the sensor and rear flange. The sensor is simply to far away. You would have to put the lens inside the camera mount to get any decent focus."
Re: PCC4K vs 6K for 16mm lensesviewtopic.php?f=2&t=96913&p=538072&hilit=+16%2FS16mm+C+Mount+#p538072