I’m surprised – can you reproduce the problem using any of the samples in GoWpfDemo? (Other than the Virtualizing sample, which inherently has the overhead of creating hundreds of new nodes and links while the user is scrolling.)
Scrolling (via either the scrollbars or the mouse wheel) and zooming (via the mouse wheel) have always seemed very responsive to me. The performance problem has always been loading large diagrams, where the overhead of creating all those elements, and afterwards maybe performing a layout, has been hard to avoid or break into smaller pieces. (But the Virtualizing sample demonstrates one way of doing that.)
Any of the regular profiling tools should work. Of course interpreting the results can be difficult.