Keekee

I’m looking to shoot a short film this month and director and I are keen on 6k 3:2 full frame open gate format using the raw recorder (with mamiya 645 lenses and kipon speedbooster for some poor mans imax) but wondering if this can also be recorded as a proxy to the SxS cards and is that still retain the 3:2 aspect and at 4k prores or xavc? Be some time before I can get my hands on Venice to test and keen to figure that out sooner. Cheers for any help.