Good thing to test also is see if you are already getting "full burn" with the current 24 inch. If you are then you are wasting money having a longer barrel put on. You would actually lose a little speed.
Good way to test is to take an OLD white sheet ( I say old in case your married..Dont wanna pee off the wife ,) ) Lay it on the ground longways toward target, get in the prone position with the end of the barrel about 2 inches from the end of the sheet, and about 6 inches up. Let a round loose and see if there is powder on the sheet. If there is then you could either reduce powder charge or longer barrel. If there isnt then the only need for a longer barrel is if you want to increase your powder charge with the same burn rate powder, or if you want to go with a possibly slower burn rate for more pressure. Some calibres do better with a slower charge while some like a faster burn. Its all dependant on the rifles and calibres.
One of the most important components of deciphering a new hunting area is distinguishing between the summer and winter ranges for the game that you plan to pursue. Without knowing this you cannot make reliable assumptions about where the game will be come opening day. Knowing these areas will allow you to take the current weather (as well as the past couple weeks) and apply that to the landscape and make an educated guess as to where you might find that big buck or bull.
There are a couple ways...