My thoughts on duplex loads are they sound good but in reality they combine the worst of each shot size. The large pellets are not needed at the range the smaller ones are lethal while the smaller pellets take up space needed for more large pellets to produce adequate pellet count beyond the lethal range of the smaller pellets. Duplex loads are a good advertising trick to separate money from wallets.
As for gearing for 70 yard shots, just how often does one see them compared to 40 yards and under plus how likely is one to connect on such a bird? And if hit, what is the odds of the bird being recovered if wounded? I personally would load/choke for shots up to 45-50 yards tops and consider myself more than adequately prepared for any opportunity I would find. I would also forget the 1.5" penetration nonsense as that is a theoretical estimation that does not take into account all the various shot presentations one can see in the field. It is going to take a lot more energy/penetration to reach the vitals of a 3 year old rooster flying away from you than an inch and a half. If you want to reduce the odds of biting down on a piece of shot, you will need even more penetration than the looked for minimum to get exit wounds.
The loads you are contemplating will probably meet my expectations for pheasants but at a much closer range. If I were consistently seeing more birds at 50+ yards I would either look closely at my tactics and find what I am doing wrong or figure the birds found an ideal sanctuary against human predators. Even then, one can usually figure out a counter that will work on occasion at least. Or, I would consider them rifle fodder as is legal in my state.
