Check these reviews:
http://www.boardseekermag.com/windsurfing-equipment-tests/5.3-power-sails-test-overview-2009-109.htmlwww.boardseekermag.com/windsurfing-equipment-tests/4.7-sail-test-overview-2009.htmlFor me personally, my 2007 north duke was a great sail in light winds when I had it on a north mast, but once I got the powerex rdm i found it quite difficult to set up and it only had a tiny sweet spot that was easy to miss. I never really felt it had a good top end cause the draft would move around a lot once it got overpowered, and you would be backhanded in all the gusts.
The simmer icon, has just got an awesome range. Super stable, and in my opinion easier to tune, you pretty much don't really need to touch the downhaul once you have it right, and using the outhaul you can set the sail up to get you going in less then 15kts, or handle gust 20kts+ days without being backhanded.
End of the day I wanted tougher sails which could handle my amateur wave sailing attempts, and the simmers were almost 50% cheaper then an equiv north sails quiver. I sail at manly usually whenever its windy cause its just the closest place to drive when you only have a few hours spare to go sailing. More then happy to show you how they rig and have a bit of a yarn