You anwered your own question. If you have to mark your yardage and stick within that range. As some have said, if you want the extra range look into the barrel and slugs that will allow you that little extra. When I comes to slug barrels I have always had the longer is better theory but on the most part like Remington and Mossberg only produce a 20 -23 in barrel anyway.
I know that slug barrels are funny and have seen bad barrels right out of the box, so if you have any grouping problems at the range with different slug types, target the barrel because it may just not be any good...