Tweaked the code some more. Sharpen set to 0.8 is pretty much the same sharpness as with no AA at all.
I also updated the blueprint attached to the camera. It sets LastFrameWeight to 0.5 and reduces Sharpen to 0.5 (the higher LastFrameWeight, the less Sharpen we need)
Here are 3 examples where I move the mouse back and forth with motion blur amount set to 0.1. Quite pleased with the result 
