20-30-40 yards are prob. the most common. Most of the new bows don't have enough drop in them to justify less than a ten foot distance between pins. I would suggest you do just like you said and see how much difference there is between pins.

Aim towards the top of the target and shoot an arrow. Then step back to 25 yards and aim at the same arrow. See how much drop there is. You will prob. be surprised at how close they are. Mine are less than 2 inches. Then do the same at 30 and there is prob. a 3-4 inch drop which if you are alittle off could put you out of the vitals.

The difference at 40 is more noticable so get a 30 yard pin set and then try the same at 40. I pratice alot at 40 but restrict my shots on game to under 30. You will be able to find your range in a short time as well.

Good Luck