The classic physique ideal is one in which the neck, upper arms, and calves have the same measurement. The shoulders are broad and the waist and hips are as narrow as possible to produce that "V-shaped" torso.
The classic Greek ideal is one in which the upper arm is a bit smaller than the neck (~1/2 inch smaller) and the calves are a bit smaller than the upper arms (~ 1 inch smaller). The waist and hips are also a bit larger than the classic physique ideal.
Although we, at CPB (Classic Physique Builder), prefer the classic physique ideal, we also value the classical Greek ideal as well. It is often easier and a more reasonable goal for a person to attain the classical Greek ideal first in their natural bodybuilding efforts. Having achieved that goal, it is then easier to bring the arms and calves in line with the neck to attain the classic physique ideal.
Check out this calculator at the Sandow Museum site (www.sandowmuseum.com/ideal.html) that will give you your "Greek Ideal Measurements" based on your wrist size.