I've seen videos on youtube with people squeezing a 20+ lb pike through a 6" hole. The only trouble with an 8" is if theres 2'+ of ice, it cant be a little more challenging, or a really cold day, and 8" hole can turn into a 6" hole real fast. Just need to play em a little.
Sometimes an 8" hole can be beneficaial, wont allow big bike to turn and thrash in the hole.