The higher the OG, the higher the FG. Plain and simple. If you can get a DIPA to finish at 1.010, hats off to you. I doubt it will happen unless you substitute a ton of sugar for some of the malt.
Don't try to stop fermentation early. There is a technique out there to do so that is popular with some cider people, but... in a beer, no, don't.
Amarillo would have been my first choice to replace Ahtanum, yep, that's good. And Nugget for Millennium, yep that's good too. Perfect.