Bindings LF Watson vs LF Harley vs LF Vantage CT

I am looking at a new set of bindings. I may be tempted to go with a New LF Harley board too. I currently have 2008 LF Lyman 139 and 2008 Vantage OT. I want to go closed toe, and I haven't ridden much in the last 2 years. I can jump wake to wake HS and TS and HS+TS 180 grabs. This year I'm going to be riding a lot more than before, and am hoping to get an invert and 360s nailed.

So my question is about the 2011 LF watsons, the Harleys and the Vantage CTs. I've read all the technical details between the different bindings and I know for example that the Flex Level of the Watsons is 9, the Harleys is 8 and the Vantages are 6-8. What does this actually mean in terms of what's easier/harder when you're riding. What is the advantages and disadvantages of a high flex rating?

And I also notice that the Vantages and Watsons come on the AR6 chassis, and the Harleys are on the IP6 chassis? Whats the difference?

Finally, people who have any of these bindings or have tested some how did they all compare/how do you find what you have?

Thanks!