I submitted my entire portfolio (400 clips at the time) to mediastock.ca about a year ago. It's a non-performing site, with no sales. So no matter what the percentage to the artist is it doesn't matter, because it doesn't generate any traffic! I wouldn't base my choice of where I sell my footage on the percentage, as most of the dysfunctional sites offer great splits. I've generated a working list of sites based on actual income produced. You can see my breakdown of this at:
http://www.stockvideoseller.com/public_html/where-to-sell/You can also access the resources section and see the breakdowns of other stock footage sellers, by following the links.