Here’s a macro that may help if the other solutions do not.
Save the file to your ZStartup\Macros\Misc folder. Press Macro>Reload All Macros and you will have a new ‘ResizeWindow’ button in the Macro>Misc subpallette.
Important Note: the macro resizes the ZBrush window to one pixel less than the screen res. It’s designed for a resolution of 1680x1050, so the file will need editing in a text editor for a different resolution.
If you store a configuration make sure the ZBrush window is maximised first. If the stored window size is the same as the macro then it will not work.
Download here:
Pressing the macro button will resize the ZBrush window. Assign a hotkey to the macro button to make it easy to use.