We're really fortunate that we have interchangeable chokes today. However, I think the only way to really be sure of your pattern is to try your gun with the load you want to use at the yardages at which you expect to use it. The old rule of thumb of testing a pattern at 40 yards isn't very practical if you're doing a lot of target shooting at 20 to 30 yards.
Changing the load can make a huge difference in pattern, even with the same shot size.