am also looking at tablets- wanted some more feedback on the size- either 6 x 8 or 9 x 12- with the 6 x 8 has anyone ever felt like it wasnt enough?
You can get by on less, you’re hand get’s used to ratio difference. I did comics with a 3 x 5 I think it was before eventually upgrading to a 6 x 8. I’m used to doing small details though, and don’t usually make huge strokes that would span the page anyway. It’s personal preferance really.
For me, the larger the better, I came from a traditional art and industrial design background, so I like to move and have lines flow - right off the page onto the table. 
I use a 6x9 for a mouse, then for work a 12x18 and I’m demoing the Cintiq 20U from Wacom in a week or two, but I can’t see not going with it. It’s just so liberating to have space - more space and more!
i have a 6x8 at work, and i miss my 12x12 at home