It looks like you will be very close to 280 fps with the Maxima arrows. This arrow (complete) is going to weigh, with a 100 grain tip,a littleshy of 400 grains. You will lose about 20 fps off the IBO by having a 28" draw length. You will also lose about 12 -15 fps by the degree to which your arrows are over 350 grains. So you might wind up in the upper 270's. You can back off the draw weight a little if need be; but I'll bet you are about right.