If I make a new floating viewport, then in Properties I change the width and height pixel numbers, I can enter any number I want, but if it’s larger than the current full Rhino window, it reduces the number back to somewhat smaller than the current size of the window. For example if my main (non-maximized) Rhino window is 1200 x 900, the max size I can set via Properties is 1164 x 798. Which seems to be more or less the width of the window minus the side edges and the height of the window minus the title bar and the status bar.
However, if i have screen space, I can drag the floating viewport border to make it larger after (even over my second screen)… Just can’t enter a precise pixel value (which might be important for an animation for example).
This is in both V6 and the WIP.