what rom are you running? no screen lag for me on a really old cm10 build. pretty much consistent framerate, though it is kinda slow
i think part of the problem here was B&N's choice of using a PowerVR SGX 540 GPU in this tablet. this particular GPU was also used in the entire original Samsung Galaxy S line, and is at this point 5-7 years old. not a particularly great GPU in my book. granted, we're not pushing a really high screen resolution (1024x600) but still, it's a really old GPU.