I had to restart my campaign last night, because I'd gotten myself stuck on the finale of the Sacred Coil-arc and Ironman-mode being Ironman-mode ... you get it, right?
So what you assestment on the best route through the investigations?
After my second start I went Progeny -> Grey Phoenix -> Sacred Coil now - and so far it is looking good. Before that I went Progeny then Sacred Coil and no matter who well I played or lucky I was, I got hammered in the encounter with the Gatekeeper.
I picked the Progeny first because I remember just who powerful psionics can be - and if you don't pack those flashbangs the Progeny really gives you a hard time.
Grey Phoenix however felt kinda weak as second pick, they didn't seem to have the same powerful combinations that the Progeny and Sacred Coil have.
Sacred Coil ... pulls no punches, but the kicker is really their finale with the waves of Ronin and then that f'ing Gatekeeper for a boss...