In ArchiCAD 8.1, depending on the VGA card driver, the area of the 3D window that falls outside the display area might not be rendered properly (either black or scattered with noise). Many VGA manufacturers use this trick to gain speed. (after all OpenGL is designed for accelerating the display).
In ArchiCAD 9 we worked it around, so the hidden parts will be rendered properly, no matter what card you have. Dwight hit probably an other graphic card limit, also card/driver dependant. My ol' intel integrated VGA has no problem with 4000*4000.
Gergely Kmethy
VP, Customer Success, Graphisoft