First lets think how the pump works, as that will help you decide, since either pump will do the job.
A Autopilot pump is simply a 12 volt pump that changes direction by reversing polarity of the power.
There is no variable power here. The pump is either off, or pumping.
If you go with a slower pump, you will simply get slower corrections. This can feel smoother but it can also be slow to react in situations where you would want quicker reactions, for example in a heavy quartering sea.
If you go with the faster pump you will get the faster reactions you would want in a heavy sea, but you will get faster reactions in a calm sea as well.
The good thing is that your autopilot computer will learn how your boat reacts to overcome the tendency to overshoot that a fast pump would provide.
On my boat with my steering ram I was near he upper end of the smaller pump and went that way. Like you I could have went with the higher capacity pump and would have been just fine as well.