I think it really depends on a few things... the size of your hand, the size of cutting boards you have in your home and what you are comfortable with..oh and the knife itself.
I used cheaper 8 inch blades for many years..mostly Chicago cutlery and always felt that they where to small but when I picked up my Shun 8 inch, the whole things feels and looks much larger..and is much larger then rest of my knives. My main board is the perfect size for an 8 inch knife, if I stepped up to a ten inch, id have to invest in a new cutting board as well.
and lastly, im a smaller guy, my hands are not giant so a 10 inch blade is just awkward for me. However my 8 inch just feels right, I have good control and it's over all comfortable..the best knife is the knife that just feels right