RDM is preferred. They're more durable. Small sails are always spec'd for RDMs. SDM masts tend to be used for big race sails.
At the spit, you'll prefer a 400 cm to use with the typical 4.5 to 5.0 sails that you would use. 430 cm would be way too stiff. I'm guessing your reddish-brown North sail prefers a 400.
More details... powerex super wave, 70% carbon, 19 imcs, excellent condition, barely used. $100 obo. Lighter than a skinny but not as strong jammed in a reef, nor as easy to grip.