Autodesk Navisworks
Default speeds are a bit of a trade off; try to go faster and you will likely see the problem worsen, but make it slower and it takes forever to get anywhere in the mdoel.
Try the far clipping planes to reduce distant objects. It's not ideal as it can strip out context but the reduction in the number of objects to refresh on-screen can help. Also maybe increasing the "Number of pixels below which objects are culled". I think the default is 1 pixel, increasing that value will cause some objects to drop-out should improve performance somewhat.
