Well, a lot of people were looking but no one was replying, so I'm assuming that meant no one had the answer.
I had some time to kill this afternoon, waiting for our Superbowl guests, so I decided to experiment a little and find the answer for myself. This may not be 100% on the dot, but I think I'm at least in the 98% range. The available resolution for the Nook Tablet's native reader is 600x880 pixels, in case anyone other than myself was interested.
Thanks, and I hope this helps someone else.