I cant let to many secrets out of the bag here, but trust me when I say the smaller the exhaust(with the right design) the better. Polishing the exhaust conducts less heat to the head(less surface area) and has a very dynamic effect on, ummm, lets call it "sonic flow conditions".(secrets I would be shot if I revealed) Beleive it or not, a multiple-championship cup team is testing a head with a 1.54 ex valve.

And if proper combustion is obtianed only a anemic ex port will be sooty