First if your broadheads are not flying similar to your field points it most likely means your bow is not tuned properly. And you need to paper tune your bow to know how to correct this. After you tune your field points and broadheads should hit almost if not in the absolute same spots. If you have a conctact problem with the rest you can simply adjust your setup, you do not have to purchase a fallaway rest to provide adequate clearance. Also feathers are much more forgiving when it comes to clearance problems, and tune easier. And yes you need to screw with your bow if it's not tuned correctly. If will prevent a lot of frustration when you shoot. A properly tuned bow will seem to guide the arrow into the target. If your bow is tuned well I don't think it is going to make a difference whether you shoot a three or four blade broadhead, but for the record most people think a three blade broadhead is easier to tune.