There is a great article written by well-known zBlock admin J3di:
He explains the origin of this issue, compares it with GoldSrc and he also suggests a solution for the "peeker's adv" problem - reverting client position accordingly to your lerp amount. If I understood it well... It is from 2009 so I really dunno if it's still actual for CS:S or CSP.
I also believe that some part of the "peeker's adv" comes from the off-centered FOV pyramid (left-sided POV - you are looking through left eye only).