Replacing valves is not mild, its quite invasive(talking about oversize valves, here). For a mild build, do a nice 3 or 5 angle valve job with stock valves then do a little mild porting work. Get good springs and retainers. Uness you're aiming above 500hp, your money is better spent elsewhere rather than cams/big valves/aggressive porting work.
by the way, this is my personal opinion based off of my experiences. You may have better results, but keep in mind having an end goal will help greatly during the descision process!
The numbers you see below in my sig are on 272's, a 67mm turbo, stock valves and head, and E-85. The head in its stock form is very capable, but when you get up there in power, then its time to start upping the ante and getting the setup really effecient to squeeze every last drop outta the engine!