According to North Sails RDM masts are not good over 430 length, as a lightweight i have 460 skinny and love it. no issues with two different mast brands at this length(Severne and Hot sails). In fact Hot sails recommend RDM mast for their 8m GPS slalom sail. I think for non PWA sailors, even 460 has lot of benefits in RDM. I'm not sure about this claim by North Sails
From the North brochure
"Not everyone
<div data-canvas-width="283.931">knows that RDM masts make sense only up to lengths of around
<div data-canvas-width="275.0400000000001">430 cm, since they show a rather soft flex behavior as a result
<div data-canvas-width="259.11600000000004">of their smaller cross section. Therefore, they are primarily
<div data-canvas-width="280.04099999999994">suitable for Wave/Freestyle sails with the additional advantage
<div data-canvas-width="282.74199999999996">that they are easier to grip during maneuvers. On the other hand
<div data-canvas-width="283.68800000000005">large, mostly performance-oriented sails need stiffer masts with
<div data-canvas-width="275.43900000000014">a “more direct“ flex. This characteristic demands a larger mast
cross section in order to ensure reaching the required stiffness"
