ideally the extension should not really be more than 30 cm so anything with a luff length shorter than 460 should work.
I used to have a 6.7m Pryde Hellcat which rigged on a 430 mast, luff length was 452 I think, the sail itself seemed pretty gutless in lighter winds but was good when it did start blowing. Since then I bought a 490 Izzy mast and an older 6.9m Ezzy Panther sail and it works a treat.
Ezzy sails have the most tuning and are probably the most powerful sails on the market.
Some sails out there are what the magazine's call slippery, this means they are not that powerful but good when the wind does get up and some sails out there are powerful but can be a handful when the wind increases. I always found with Ezzy sails, especially the older ones that they feel heavy on the beach but once on the water they are powerful and more stable.
I found the Ryde to be not a bad everyday sail, but it has limited range, when its too light it lacks bottom end power and shape to pump well and when over powered it shape shifts like an alien, with the center of effort moving wildly making it hard to lock in through gusts. Also as others have said, like many sails they are very dependent of the correct mast curve. I persevered for far too long with an older NP mast which by the numbers was correct but when I upgraded to a newer one found that my sails suited it far better, no idea what exactly was different but easter to rig, more forgiving and generally felt more powerful.
+1 for ezzy sails. I have a 7'5 cheetah, 0 cams freeride, really good for me and really good build. I find an old 6 infinity 2 cams freeride (now lion) for higher wind that go really well too. Thoses sails need 460 mast for 7 and 7'5, but as David Ezzy say their sails can work on wide mast range (CC) so you can probably use it with your 430 and extender before find a 460 on second hand market.
