There is no way I would recommend decreasing pattern density for a follow up shot. Those Hevi-13 #6's will have more killing range than you have pattern density. If you don't get them with it the first time hit them in the head the second time and it is a done deal.
The 2oz offering is quite superior to the 1-5/8oz load.
If you are going to be using the factory full choke you will probably increase your range (by increasing pattern density) a bit by going to the Federal Heavyweight #7's with the Flitecontrol wad. Might want to give them a look.