I sounds like you are using the zoom selections from the button on the bottom of the sheet.
I'd like to know if there is a way to control how much the zoom changes when I use my mouse scroll wheel. It seems to jump from "way too big" to "way too small" with a single nudge of the scroll wheel. As a result, I typically have to use "way too big" and do a lot of panning around.
Is mouse zooming tied to the button zoom levels, some mouse setting, or something else?