I've posted the latest project files 208030920.
I've fixed all the shader issues and put bandaids on the transform problems.
I've also stuck a flag in the code to switch between glGetTexImage and PBO transfer (GPU -> CPU) at the top of GPUVectorField.cc.

Results:
Primary vector field tex (not read back): 1024x1024
2 Secondary data tex's (for upload and readback): 64x64
Render timer set at 1k fps

With glGetTexImage: 75fps
With PBO transfer: 100fps

I'm pretty happy with it. Even with the glGetTexImage() simplified routine it's pretty snappy (though I'll still make the PBO thing a requirement anyways since the other features need OpenGL 2.0)

Edit: One thing I learned doing this is Async PBO read back doesn't work unless OpenGL multithreading is enabled.