It probably depends on what sails you have or plan to buy. If the you have sails that recommend a skinny mast then look at getting one. Otherwise don't worry about it. Perhaps if your current mast breaks look at getting a skinny mast as that seems to be the way things are going.

Yes skinny masts need a new extension. Normally the mast will come with a boom sleeve. I don't think skinnys are any lighter. They might be stronger.

The main differences for me going from SDM to RDM was its easier to get the mast up the luff sleeve when rigging and an RDM is easier to grab in transitions.

What type of sailing are you doing and what is your weight?

For waves there is no doubt that the RDM are more durable and all the current sails are designed around RDM masts. So if you were buying a new mast it would make sense to go RDM.
If you are more in to blasting around on flat water the need to change is dependent on what you want from your sails.

As a lighter weight sailor (75Kg) I like setting my Loft race sails on RDM masts for a few reasons.
I like having less gear and use the same mast for wave and race sails.
I prefer the handling feel (not to grab the mast as this is a bad habit) and balance of the rig with an RDM.
I find the rig breathes better in the gusts allowing me more upper range out of the sail.

However if you are a heavier rider you may dislike the springier feel of an RDM (particularly in larger size sails) and the reduction in low end grunt.

So if you have a serviceable SDM and just want to blast around as a heavier rider in lighter winds then SDM may be better.

Rdm is definitely the go!

So much stronger

I too am looking to buy 6.0 and 5.0 sails, mast and boom

In pure engineering measurement, for the same weight of mast, the larger diameter of a SDM compared to a RDM will have
- Higher moment of inertia,
- Will be stiffer and
- Have a higher bending moment, shear and compressive strength

Presumeably, that is why they are still exclusively used for large race sails.

I also used SDMs for wave sailing all through the 80s and early 90s. However the current trend is for RDMs for these sails

So there must be some other parameters / advantages that have made RDM, today, preferrable over SDMs for wave and freestyle applications.

So what are these advantages?

The other advantage is that wave sails these days are designed for RDM's.
Aside from better performance with a RDM in a lot of them you won't be able to fit an SDM up the luff tube.
Wave = RDM
Slalom / Race = SDM (mostly)

Skinny.......and no other.

Why...No idea

Pros....their skinny

Cons....their not fat

Seariously though I don't think it makes all that much difference unless the sail is specifically for one or the other. For basic sailing any will do, just because they are skinny doesn't make them lighter but I think (nothing to back it up) they are stronger. I've seen SDMs snap on the beach in the sun, not so for the RDMs.

That said I switched to RDMs within a year of starting to windsurf and haven't gone back but I don't use a sail over 5.8 so that could be the thing. Most bigger sails rig on a 460 and I don't even know if they make RDMs in 460????

If your most used sails are 6.2 and below I'd personally go with the RDM but if your on bigger freeride sails then go with the SDM.

Go for the best carbon content you can afford though, I think that'll give you your greatest gain.

....Sorry for the ramble as I've had the sweetest day on the water and I've celebrated with a few brewskis....BURP....Mmmmm, Beer.

Skinnies if you want peace of mine .