i think every one responding has touched on parts of your questions, maybe we can get all those thoughts together in one post. First; you should run the variable speed at the speed needed to do a good job. Over speeding them will only throw cobs around and wear parts out before they need too. It is about like running a reel, some were even set up with auto reel speed unit to control. Run the header according to ground speed and crop- conditions but that is a judgment call for the operator. If clean grain is limiting factor you need to check some things. Check the paddles for size and condition, and yes the poly ones seem to carry more grain. Check both the auger in the grain bin and the bottom cross auger for wear. replacment flighting can be installed if you do not want to replace the augers.be sure and check all belts and sheaves. any sign of slippage will limit full capacity and you are right up against full capacity it sounds like. That belt behind the cylinder drive belt on the left hand side is critical. Make sure that the belt is in good condition and that belt has not bottomed in either sheave. Often times the idler arm pivot can be the problem. make sure that the pivot bushiing is not worn and that arm moves freely.One other thing sounds simple but can be a problem, check the sprockets on elevator and be sure they are not spinning on shaft. good luck vstk