Any other ideas?
rotate - matplotlib text box .

linespacing: float (multiple of font size) multialignment
a matplotlib.figure.Figure instance: fontproperties or font_properties: a matplotlib.font_manager.FontProperties instance: gid: an id string: horizontalalignment or ha [ ‘center’ | ‘right’ | ‘left’ ] label: string or anything printable with ‘%s’ conversion.

How to rotate matplotlib ... My x and y ranges differ by orders of magnitude, and obviously the apparent slope is affected by viewport size among other variables, so a fixed-degree rotation doesn't do the trick.

I came up with something that works for me.