Hi,
that is a nice question, but you can think of it this way
For perfect dielectric (no losses) tand = 0
For perfect conductor (no losses, if you like to call it this way) tand = inf.
The losses of the medium depends on where the current will flow. For lossy dielectrics, the current (if you consider it conduction current) flows in the bulk, so you will have some losses = sigma * E . For perfect conductor, no current flows in the bulk, that is why you do not see losses in perfect conductor. For normal metals, the current flows mostly in the surface, and a small fraction in the volume, which causes losses (this is what is called the surface resitance of metals)
regards,
Adel