I just finished tweaking the Acros in Caffenol C and yes an EI of 1600 is very possible, as the sample image below shows… 3200 is just a tad past my liking but for some shots it would be usable. Click on both images to see a larger view.
The dark barn boards above the windows were placed at Zone 3… they were EV 0. The detail outside the window fell on Zone 14. The detail image below is a 3″ x 3″ crop from a 20″ x 20″ print… pretty impressive.
My metering technique for these images is a stripped-down Zone approach that will be outlined in some detail in my next book The Photographers Coffee Break … I feel it fits the Caffenol C process quite well.