if you run big deadbaits on quickstrike rigs... you will get your quickstrike rigs caught up on the bottom of an 8'' hole... it can be a really crappy deal with thick ice. If it hasnt happened, its gonna. 10'' greatly reduces that chance. Also when its extremely cold and your hole is freezing in, you end up with more like an 8.5 or 9 anyway with the 10..
If I wasnt a pike fisherman, specifically targeting 20# pike, I would not use a 10'' auger. And I will agree that big fish will come up an 8 inch hole. 20+ northerns will come up without much problem. 9" is really perfect in my opinion.