You can actually use any dpi setting you like. i.e. \112dpi etc.

Regarding the quality. The way to resolve this is to increase the dpi setting to say 300, then show the image at 1/3 height. This is you can do by adding the height=" " attribute to an image, but the challenge is knowing what height to use, since an equation size is not constant and it difficult to guess. We will, however, very shortly be introducing an enhancement to the editor to work all this out for you, giving you the ability to scale equations by a set percentage.