There may be no right or wrong answer here. Everyone makes a good case for their preference. I have 6.5" full range drivers (SET powered), crossed over to super tweeters at 10k and an 8" sub. I don't need anything more than the 8" sub. Within the limitations of the system and room (garage) it has plenty of oomph. In another system I have speakers with 10" drivers. I don't need more. I tried a 12" sub and could plainly hear it down the hall but not at all in the room itself. But an 8" driver wouldn't be satisfying in that room with my taste in music. So within the confines of that system and room 10" is optimal. If I had a dedicated room with full treatments and optimal dimensions I think I would want and need 12" drivers because they are so much fun..
