oversized valves wouldnt hurt if you are getting a good port and polish... ive been told that getting 1.0 mm over on the exaust side is a good idea, since they take most of the heat... anyways, its a good idea to get them now, that way they will be taken into account when you get your port and polish, and your 3 angle grind on your valve seat... either way, your valves will need to accomodate your valve seating... are you going na or are you boosting???