I've made a lot of pastrami over many years, mostly from scratch, though from time to time I'll start with a refreshed corned beef. When it comes to cooking it, I smoke it at 200°F to an internal temp of 160°F-165°F then cool, wrap in foil, and refrigerate overnight. The next day, I put it on a rack in baking pan with some water, wrap the pan with foil and gently steam it for 3-4 hours until the internal temperature again reaches 160°F-165°F. Comes out perfect every time and I have never understood the need or rationale/reasoning behind why some advocate to smoke or steam it to around 200°F.