I have found that shooting a more open choke will help long range performance,as well as sometimes over all performance.

Also reducing the amount of shot going through a tight choke will do the same thing.There's less to squeeze through the choke.When you go to the HV shells you are dropping shot weight.Like the 3.5" Win XX loads are 2 1/4oz..and the 3.5" Win HV loads are 2oz.They may also use a different powder or shot cup in these HV loads...I'm not sure,but I'm suremost of the new found speed comes from dropping the load size.

Rhino's can go tight because they are sized for primarily smaller shot.60% of the 4x5x7 nitro loads are #7's...so you can use a tighter choke.

I have also found out the same thing goes for buckshot.I get my best patterns at longer distances with Win 3.5" 00 buck(18 pellets)..with a Modified choke.I was suprised that it did better than a full choke,but it makes sense.You can only squeeze so much through a choke.When the shot size is too big,or too many come through at once they will squeeze down tight,and it will cause some of the pellets to flatside(I'm talking lead).Then you'll blow the pattern.Hevi doesn't compress as well as lead,but it will still blow the pattern if thereis too much trying to go through a tight choke,and that's why for a 12ga with standard barrel(not overbored,or back bored),most choke manufacturers recommend a .675 choke constriction for hevi shot.

I say it's worth a try to pattern your gun with a looser choke.