The handouts and speaker's copies are generated by the dbslidehdout.dsl stylesheet. The printed output for slides or overheads is generated by the dbslideovh.dsl driver file. Edit these to change:
the page size and orientation
the margins
the base font size
the relative font sizes of larger and smaller fonts
the line spacing
the fonts
Again, you're not restricted to what appears in the driver files. You can override or modify any function or variable in the DocBook print stylesheets.
Another way to tweak the output is to modify the Jadetex macros if you use the TeX backend. This is certainly not for the faint of heart and requires some TeX knowledge. We have already done a very simple modification when we got rid of the "every-other-page-is-empty" syndrome.