I really cannot recommend a font size for the window size, not a designer, just a coder ^^
But it is strange for it to be blurry like that. The reasons I can think off is:
1 - Make sure the smooth is set to disable on the plugin parameters.
2 - Make sure the window size and the line height of the window does not have decimal numbers like 300.05, etc.
Because seems to me that you are using a plugin to mess with this windows. The best test will be first check if that is not the problem, therefore, disable those plugins and see if the font will render nice on the default windows.
