Get the Navionics Premium East, and when you do get on and register on the Navionics web site so you can download the Navionics Web Store and the Navionics PC App. You will be eligible for 12 months of map updates to your map card. I can't believe the additional data that I have received for Old Hickory and Percy Priest. They release mapping updates weekly.
http://www.navionics.com/lakes/freshest_data.html