As far as empirically finding the optimum group size, it'd be cheaper to find the number of researchers in a scientific sub-discipline and measure the productive work they do in that field. They are teams that review work for general distribution, read on others' progress, and contribute to the discussion. Larger sub-fields that would be more efficient divided up would have large incentives to do so, as defectors to the sub-sub-field would have higher productivity (and less irrelevant work to read up on).