With all due respect to the cited pitfall reference, in most cases the viewport is entirely adequate for clipping the rasterized pixels since the viewport dimensions form the last stage in the 3D-to-2D transform. The unusual case in the pitfall example actually refers to certain boundary condition vertexes disappearing since clipping is actually determined by the perspective projection planes.
However if your model is entirely visible within the viewport this is not going to happen. In no case will pixels ever “bleed” outside of the viewport region so you wouldn’t have to consider scissoring.
Also what you might consider creating borderless child windows to compose each of the visible views within your main window. In this configuration you could eventually create separate GL rendering contexts for each subwindow and leverage muti-threaded rendering, which is what 3DStudio does for multiple views.