You want a 1 pixel (px) border around each UV island at the lowest visible MIP level which means 2 px between islands:
So baking a 2048² map (where a minimum of 16px is recommended) the gap/gutter between adjacent UV islands should be 32px. and if you are baking to non-square textures, the largest dimension should be used to obtain the minimum distance value needed.
For smoothing you will want to smooth the mesh based on your UV islands. This means that all vertices not on a border should be averaged (smoothed; edges softened) whereas all edges/vertices on borders should be hardened. In 3DS Max this means separate smoothing groups for each UV islands, whereas in Maya this means softened edges as described above.
UV Unwrap - Hard Surface - Maya
UV Unwrap - Hard Surface - 3DS Max