Yup. I happen to know some road race engines that run several degrees less high rpm timing than dyno or drag race tests would indicate. A fully heat soaked engine is definately a little different animal. No one I know runs alum heads road racing these engines, but that's a function of the rules. No reason to develop something that's not allowed. I know some cars driven on road courses (non competition) have used aluminum heads. Also seen some problems. But I would not make any generalization about that because every new use, especially max effort stuff, requires development. For those not willing to put the devlopment time and money in, then go conservative.