It's generally down to what your used to using mate. I use a 1.3mm tip with a 110 air cap.

When you say the finish is not as good lately, how exactly do you mean? As in it doesn't flow as nice? If so that could be down to the change in gun/setup (if it's happened since then) It may take some getting used to, i used a different gun to paint a mates car and i ended up having to flat it.

Keep using it and see how you get on, as long as the jobs are at a standard where they will polish at least it's not too bad