Wow I just read that too. I've been using an 11x5 'cause that was the size that came with my Nexstar, and it seemed to work really well. Maybe I've just been really easy on the motor, so I noticed a big change with the 12x5. If the manual says 12x6-7, I should be fine. Wierd, but I liked having the RPM's and the engine running cooler.