I always hone by hand, and I can hold my 8"x3" Shaptons and Naniwas (with bases), or my 10"x2.5" Charnley Forest (which is on a big wooden base) in my hands. Just not all at the same time lol..!

Then again, I have big hands..!

My coti/BBW combo is actually quite small though. Its 6"x2", and I almost find it a little bit too small..!

But to answer your question, the only thing to ensure is that you can get a good even coverage on the blade with your stone. You dont want it so small that its hard to keep the razor flat, and you dont want it so big that its like trying to hone on a paving slab. Other than that, its really personal preference..!