Just remember it won't matter one bit how big your exhaust valve is if you can't get the fuel/air mix in.. You will just be wasting space with an over sized Ex valve if your In valve (or whole intake system in reality) isn't capable of getting it in.

Or putting it very simply, why have a 110l/m exhaust hose when your intake hose can only do 90l/m, you are better off balancing the flow so you get equal amounts in and out..