Best engine temp for horse power??

My second run is usually my fastest. This is probably due to getting all the fluids up to temp during the first run (trans, engine, rear end). I always dial from my second run. However,when I start to hot lap in the later rounds it also picks up a couple hundredths (if there is < 20 min cool down)....so who knows. I usually hit the water box at 160° engine temp.