British loads were designed for a different game than American walk up shooting. Lighter loads make sense for smaller game like grouse, woodcock and quail, and high volume incoming pheasant shooting, but not for going away pheasants.
I would wager that an active driven pheasant shooter in the UK kills more pheasants in a year than most American hunters do in a lifetime. But I am not that is relevant to deciding if loads designed for driven shooting are useful for walk-up shooting. Breeks may be handy in the moors but not so much in a New England thicket.
