Pokerstars vs. Party rake structure (rakeback related)

[SinCityGuy]

With the lower rake structure at Pokerstars, you are paying less rake than you would at Party.

Has anyone worked out the numbers on what this would be equivalent to in terms of rakeback? In other words, you aren't getting rakeback at either site, but playing at Pokerstars makes it appear like you're getting X% in rakeback when compared to Party because of the lower rake structure.

What is X equal to?