In theory, you will achieve the best results by getting your graphics to move in full-pixel increments per frame, especially for vertical movement. This will require some maths 🙂
For example, if you text box is changing its y-position by 300 pixels then you will want this change to happen over 300 frames. So your keyframes will need to be 300 frames apart (i.e. 10 seconds at 30fps) If that’s too quick, multiply the pixels by a whole number (2 or 3 might work), giving you 600 or 900 frames, so that it slows down by half or a third.
I would also note that FCP-generated text also will look better on an interlaced external monitor than it will on your computer screen.
Hopefully this will make a difference