I installed an SP-70 in my Albin. With the larger pump. I don't remember the volume, but I measured my cylinder at the time and went with the larger pump. At the time there was no price difference.
I think the only downside of the smaller would be a slightly slower response time that likely would not be noticeable at 7 knots.
I went with the SP 70 because I don't have any space on my upper helm to mount a control head. I mounted the bracket for the handheld just below the dash vertically and its easy to use either in the bracket or in my lap.
The plug for the controller is in the middle of the flybridge so the first mate can use it to steer (dodge) from time to time so I can take a break.
I bought a second station plug and mounted it at the lower helm in case I want to bring the control head below.
I don't know what else you need to know. Ask.
Now I see you have a Mainship 1. You can use the smaller pump. That I know.