Some Performance Optimization Questions

Tosanu

So I've been looking into optimizing my game's performance as I go, and I was hoping to get some quick questions answered that I was unable to confirm in research so far.

First, does over-resizing assets add to performance lag? I mean changing the prototype's size from the size of the uploaded artwork, or instances from the prototypes size. Some experiences during my work on this game have suggested that possibility, so I was wondering if anyone had any thoughts.

Also, speaking of artwork, the information I read was kinda unclear. Is there a specific art file extension that we should be using for maximum efficiency?

The last question is about particle emitters. They seem to have some issues displaying more than 2-3 simultaneously before my computer editor shows a frame drop. Is that my relatively low end computer's issue, or a Gamesalad limitation?

Thank you to anyone who can assist.