It's a tough call on how many actions to pick up here versus when to start greening. Count, Soothsayer, Cutpurse, Bureaucrat, and Monument are all good for Duke games/slogs.
Tough one. I tend to like Soothsayer a little more than Bureaucrat in these games.
So what about this: open Cutpurse. Go for two Soothsayers (for the Gold gaining over the game, mostly), then buy Duchies on $5+, money else, then when Duchies are gone, go for green (Dukes, Silk Road, Estates).
In a mirror, even if you lose the Duchy split 6-4 because Robz bought a Count, I think the Gold gaining will set you up for grabbing more Dukes/Silk Roads to make up the gap, and up to 10 points from curses wipes away the point advantage from splitting the Dukes but losing the Duchies. I also wouldn't worry as much about NB, then either. Maybe it'll catch a gold, but it could also flip two green and hand out a Copper; yay! I don't think I'd buy any over Silk Road.
I just don't see the Province player ending the game before you rack up enough alt vp to overtake them with good play. Every attempt to block you out of an alt VP card slows them down giving you more time.
Simulation challenge, anyone?