I am using the 5.6 S1 and a 5.0 Blade as my 2 sail quiver for summer. I think that even though they seem quite apart in size the 5.0 has a wider tunable range than the S1 and will be enough for those days when there is a 14-18knt NE. You can really depower the Blade to make it equivalent to a S1 4.7 with enough downhaul. The 5.6 S1 is light enough and very flicky / manuverable so for those days when the NE is marginal or early in the session it would be a good size. When the S1 gets overpowered it keeps its shape but develops a lot of leach flutter.

I think your choice is a good one thinking about the type of conditions we get in Sydney. Also note that the mast extension setting for both sails is the same (you can set it at 27cm and leave it) making rigging so much faster.
I sail a 76litre and weigh 70kg

hope to see you on the water.

I run the Blades, have used the S1's a few times, the Blades have a big wind range and you can sail them overpowered without to much hassle, they have heaps of grunt down through the bottom of the sail, i found if it's gusty like some east coast breaks can be or scarbs, they can get me through the break, even under powered they still feel like there driving what power you have into the board.

I found the S1 good, lite and heaps controlable when i was powered up, but being a heavier sailor in lulls i felt like the sail lost a bit of that drive to keep me plugging out..

The New Blades have lost a heap of weight this year, so rig weight should not be much of an issue..

The bottom line is if you like a flater sail or deep profile sail, both Blade and S1 are excellent sails just need to find the one that suits you and where you sail..

I cant wait to get hold of some 2010 Blades

After looking into this a bit more, I've come to the conclusion that i'll be changing over the 5.0 blade I have to the 2010 versions and picking up a 5.6 S1. (Seeing as I use my 5.0 90% of the time). The 5.6 will be there to get me out when I would be thinking of going out with a 5.0 cause its my biggest sail and there seems to maybe be enough wind up to get me out..... The sails are both "quoted" as being lighter, and less weight when the wind is marginal can only be a benefit....

thanks for the feedback - v.much appreciated