Crower makes oversized valves btw. .5mm over. It's about the biggest for a SOHC motor.
The bigger you go in a port job the less low end power your gonna have. So your not gonna want a massive port unless your going SC or turbo. It just wont help you.
If you WANT to go turbo, don't go with oversized valves. I don't know why. Skunk2 says don't do it.