Have you heard on the beach or read a forum thread, a story of a professional slalom rider, that had measured up all his masts and the difference of the mast in bending curve and characteristic was so huge that only a third of the mast where usable?
I believed a bit in that story and when I have read some Magazines test that also between the lines says something that support that, it could be some truth.
So the myth is that buying a 100% carbon mast is a lottery.
But the thing is that I never have felt any difference between masts from the same make with the same specs. I decided to make the test myself. Nine 490 masts and seven 460 from all together seven different production batches. A strap, a table and a fence, 15+10 kg water tanks.
Starting off with the long 490 masts. With 25 kg at the ferrule (the middle); not any difference at all, about +/- 1 mm. Except one masts that has been pre-bend (happens when the mast is in the sail for a week with some downhaul). But when turning it upside down, the same bending curve as the rest. The same results with the 460 masts. Then loading the tops with 15 kg. The same results. Not even the RDM gave different results, or 490 or 460 RDM. (Yes I have Loft 490 RDM!)
I kept on until I found one of my oldest masts, a 460 slightly a bit stiffer than the others. But the difference was about 8 mm. I would say that it is not much enough to feel when sailing.
Conclusion. At least with the mast I use from Loft, it doesn’t matter which mast I take!