You can put larger images directly into your listing without supersize but that means a small screen user will get fed up an move on, better in my view to use supersize to allow interested viewers to select it at will. Usefully Auctiva's supersize displays the image in a new window from where you can step through the others for that listimg.
Either way only upload at the maximum necessary size to speed up the transfer, also consider whether any small items will look better magnified or not.
