Do not overlook that there are/had been developers designed for continuous tone photography with microfilms.
Originally Posted by David Lyga
There even had been a developer specially designerd for the Kodak Imagelink HQ that yielded EI 25, though at a somewhat reduced exposure range.
With other high-reslolution films and their proprietory developers EI of between 20 and 40 are gained.
Bear further in mind that the Kodak Imagelink will no longer be manufactured but substituted by Agfa films sold under the brand of Imagelink. Thus one would have to adjust processing to the Agfa films anyway.