I've had LS dedicated with 106sv and 126sv now. That being said, I think 10 or 12 inch is plenty depending how high your mount allows you to move the graphic up in the air. I have the beatdown ultimate mount and I can get the graph 36 inches high.

IF I was buying a new system from scratch, I would go with the 1222. Having the physical knob to adjust how far out your LS is scanning is really nice. I usually shoot 25-30 ft out until I find fish/structure then scale is back to 20 ft to get an idea what size the fish are. Having the physical knob for this is really nice, but not that bad with touch screen.