This applies to HOT SAILS MAUI sails only:
RDM masts are used on all Hot sails, including the speed and slalom sails, because they're made to work the best with the RDM's. Offcourse you can also get really good preformance out of them with SDM masts. My first sail was a 4.2 SO and i used a SDM mast. Then i bought a 5.0 SO (same year) and i put a RDM in it and the difference is BIG. The 5.0 is really easy to control, works really well when overpowered, it works really well in gusty wind. the RDM gives it more drag because you create a bigger ''baloon'' in the sail. The 4.2 is very direct, feels heavy although it is much lighter than the 5.0 and it doesnt handle as well as the 5.0 even though it's smaller. BUT despite what I've written about it, it still works very well and it's good when the wind picks up.
This applies to ALL sails, no matter what brand:
The difference between a mast with C50% and C100% is amazing. I didn't belive it when i first heard it but then i tried a c100 mast on my sail (i used a c50 before). Since then I use masts with at least 75% of carbon (im still not using 100% carbon SDM's because im afraid of breaking them). I've also heard people saying that 75%:100% is like 75%:0% carbon.
I've found an interesting article yesterday about the masts. its on
(the article i'm talking about is called ''mast debating''
Hope this helps...