Some really great battles to study regarding all this would be, first, the Battle of Poltava (only because so much has been written about it, including the Russians using a 5 rank formation for its battalions) and, second, the Battle of Waterloo. Featherstones book on Firepower (not sure of the exact title) is a good one. And it lends some credence to what I've seen written in this thread so far.