unfortunately I dont have the 45 but I have held the fullsize one (8.05"length, 5.5"height)and own the 9. I was interested in the midsize 45 (7.55", 5.5") which is only .05" longer than the 40 and 9. I think it would be sweet to have the 9 and (almost) matching midsize 45 to go with it.
In my opinion the fullsize 45 felt the same in my hand as the 9 (which is the same as the 40). Im not sure if the grip is exactly the same but it felt like it to me. I would assume holsters would be interchangeable.