Viking is slow, when navigatingo on the map, while a GPX-file is loades that contain serveral thousands of points.
It seems that it is drawing every point in view, even though they probaly will be rendered as the same pixels (this is when you are zoomed out), and here it is slow. But if you have the same data loaded, and zoom in such that there is only less that 100points or so, it renders quickly.
My suggestion is to make some sort of way to not render serval thousands points, so only render points that is determined by distance (depending on zoomlevel).
I use Viking 1.1 on x86_64.