What is more cost effective? larger equipment and get it in a few days earlier or fewer pieces of machinery and save on purchasing and depreciation and interest.

That's a very easy question if you look at the economics of corn production in this area and most others also from what I have read. There are basically three factors which are under your control which have a major effect on corn yield. Planting date, planting date, and planting date. Another thing that matters is how early you get it planted. The differance in cost is negligible between the big planter, big field cultivator, big fertilizer rig and the big tractors to pull them compared with equipment and tractors half the size, especially when buying used. Same holds true only moreso for combines....the upkeep cost will likely favor the larger machine because it will only require complete rebuilds every few years instead of every year.