It depends on the CP. If the CP needs a 3", then use a 3". The problem is that the 60/1 will not work with some older trackballs without an upgrade or special adapter.
If you want a new 2-1/4" trackball, Arcadeshop sells an Imperial for $49 that I've used before. of course, I did have one out of the six I've tried that didn't work with the 60, but did work with Centipede. of course, the replacement they sent did work, and it was the same brand...