I hope it helps. I'm not playing much and it contains data from jan-set 2007.
Pacific numbers were kindly provided by RedBarracuda. As you may know, Pacific rakes uncalled bets.
As you can see, the looser the site is, the higher is the rake paid.
There are some significant differences and you must consider your style before choosing a site. Cryptos US$ tables are great if you like to bully weak tight players, Pacific is plenty of fish and Prima, imho, has the best rakeback x softness ratio available now.
I must disagree to BK. Of course what is really important is playing good poker but rake is money and I think you should consider every single number involved before making a choice.
When not on tilt, I was running at 27/18 so I must have paid significantly more than someone who runs at 19/16 for e.g