So based off of what Raymarine lists for their drives' vs boat displacement, there are two options: a linear fit, or some exponential/polynomial variation. With linear, a 8" arm will equate for a 19.2klb boat where as a polynomial fit would equate to a 21.3klb boat.

So with a 8" you would be close to or at the limit to what Raymarine would consider the Max displacement of their Type 1. Where if you went with a 11" say for example would equate to 26.5klb linear and 25.4klb poly, which at the worst would be rated 4k or 2 tons higher, which would equate to less power required in heavy seas.

Not sure how you mean to turn in her length, but we get in and out of our slip no problem with a 5' davit and ~60' of horizontal clearance to enter the slip (so she still turns about the same).

I only had to move the stops out 1" to meet (just before the ends of the autopilot). Before the install I could turn the wheel helm about 3 times over in a direction and after the install it goes 2.75 times over so not a huge difference.

Hope that helps?