Just guessing here, but I would go with the 60-75s and a 100 grain insert. If you have access to a cut-off saw or you are close enough to get to a shop that can cut them, I'd bare shaft them starting with 30" or so. If you leave 'em a bit long you can always work your way down until you've got the right combination. Best bet would be to buy one shaft of each size and work from there, but if you are mail ordering that could be a pain. With a centershot bow and over 300 grains up front (200 grain head + 100 grain insert) I am GUESSING that the stiffer of the two will work for you. Good Luck>>>-------->
Mike