There is another interesting forum I belong to called ShotgunWorld that is basically only shotguns, Skeet and Trap along with a bunch of other shotgun related areas. You should go there sometime and look up "porting" you will see hundreds of posts regarding this subject. You will also find that 9 out of 10 people that have porting say it does little if any good, save your money and shoot more.
I have a Browning 4 barrel set I use for skeet. One time at a big shoot there was a gunsmith on site that did porting. Between events I had my BOTTOM barrel ported thinking it might help with lift and recoil so that my 2nd shot could be faster and with less adjustment. I went to the next event expecting some improvement. Personally I saw none that I could tell except the gun made more noise. Porting of a shotgun doesn't work like a rifle, there just isn't enough high pressure gas to allow much if anything to happen. I now have personal experience and all the science didn't seem to make a difference. Am I glad I ported,, yep,, did I waste my money,,, yep. Would I do it again,, Nope