If I need to sear anything that big, I put my baking steel on the grill and use it as a plancha.
But really, the center cut of the tenderloin isn't that big and you could sear it in a large skillet. If you're dealing with a whole tenderloin, that's where Activa can come in handy. Trim the membranes, cut off the ends, dust with Activa and stick the ends back on and roll up in plastic wrap so the entire tenderloin is the same thickness. After a night in the fridge, you can cut it in half and have 2 pan-searable "center cut-looking" tenderloin roasts. That's the route I'd take if I was going to serve a tenderloin roast for the holidays.
