opening a very simple dwg from autocad with a few floor plans the viewport was almost unmovable when zoomed out for an oversight. zooming in into details increased the speed to kind of normal.
the same file opened in rhino 5 works blazingly fast without changing a thing. so i found out that it contains a couple of blocks, 84 to give it a number and after exploding them the viewport reacted normal in V7.
i can not share the file since its confidential, at least i can show a low res screen shot to give you an overview of what i am talking about.
maybe it is related to this topic