I was having the exact same performance problems you mentioned, as we also work with GIS and I was trying out Direct2D to see how it behaved. See here: http://stackoverflow.com/questions/4055456/is-tdirect2dcanvas-slow-or-am-i-doing-something-wrong

At best Direct2D ended-up being a little faster than GDI, but not significantly, when working without anti-aliasing.

OpenGL on the other hand allows for real-time rendering (~70fps on the same PC) of our geographic data with 4x anti-aliasing.