5oz is always a good rule of thumb, but I always find that my beers get over carbonated when bottling with 5oz of corn sugar. I would suggest that you use mr malty to get the carbonation for the style. Yes, hefes tend to be higher than the average beer, but my last wheat only called for 4oz of corn sugar. That last oz would have made it too sweet or over carbed........at least that's my 2 cents