Gillette G3 Fatboy and a Crown Super Stainless (7).
The Feather (only for 3 shaves) is my top blade in my Timeless Titanium 0.68 and my ATT M1. In my SS Blackbird, I prefer Nacet, GSB, Personna red, and Personna lab blades. YMMV but given how you already use Nacet and other blades, I urge you to give those a try as well in your Blackbird.