Based on some hemocytometer counts I have recently made, I would guess harvested S-05 is around 1.5 billions cells/ml. Low flocculating yeast is around 1 billion/ml on average and high flocculating yeast compacts to just below 3 billion/ml on average. S-05 isn't the best flocculator, but I haven't measured this exact strain.
Also, the conditions in which it was resuspended (how much liquid was remaining) obviously play a big part. My numbers are based on trying to decant as much beer as possible, then having the yeast settle out for more than 1 wk at 4 degrees C.
I would use the 1.5 billion/ml and apply it to the standard thought of pitching 1,000,000 cells/ ml wort / degree Plato of whatever beer you plan on using. You may or may not need a starter.