As i said i use an older release of cudaminer. With the more recent releases Christian changed the memory allocation, so my values won't get you anything mostlikely, other from the fact that you can get more out of your card.

if no one else has some more up to date values for you, the way to go is trial&error. Run autotune or benchmark with different L values and see what happens.

For the 3D mode im to noob to understand how it works, but several people observed that opening a browser seems to enable 3D mode for more performance (don't nail me on that though)