There's also the problem that some cuts cook faster than others, but mostly with steaks and the like it's a question of thickness.
It's worth noting that you can cook a thick steak quite slowly -- like 200 degrees -- until it's just a hair underdone, and then sear it in a blazing-hot pan to get a good crust. I mostly find that this is valuable with a VERY thick cut, especially one a little bit uneven like a chateaubriand.
For blackened fish, I use the method of its inventor, Paul Prudhomme. Turn on maximum heat -- he uses a direct propane jet, actually -- and wait about 10 minutes until you see flakes of white ash in the pan. If unsure, wait another 5 minutes: heat is everything. Season your fish, dip it in melted butter, and drop it in the pan. Ladle some more butter on top -- watch out, because it may flare. After 2 minutes for a thick fillet, flip it over and ladle more butter. After 2 more minutes, remove to a plate, ladle on some butter, and serve immediately. The outside of the fish should be lightly charred all over, and the inside should be just done at the core.  |