When we bought our boat we got quotes from 3 sailmakers. In the end we went with North Sails and 3dl sails. The price was about 18% higher than the other quotes we had at the time. One of the competing sail lofts gave me a hard time when I declined to purchase their product and said that the 3dl sails would not last 4 seasons. Well, the original 105 jib is still fine although no longer the primary head sail going on year 10. The main began falling apart last year although we could (and would) have gone another season with it if the deal we stumbled into had not come up.
The shape of these sails (although I am certain not exactly what they were when new) was pretty amazing. Especially given the fact that they had been through 3 Newport to Bermuda races. They look better after 9 seasons than other sails I have owned looked after 3 years of easier sailing.
In fact the last tri radial we had built for the Whistler was looking pretty sad after only 4 seasons (shape was awful, a big bag!). That sail had been built by the loft that told me the 3dl would not last. I believe that sail would have ultimately lasted longer but the shape was so bad I would have wanted to replace it anyway... You talk about tenths of a knot speed difference but that 4 year old tri radial simply no longer sailed to weather any longer and we had lost about 5 degrees apparent while hard on the wind compared to when the sail was new. That adds up to way more than tenths and worse yet more motoring...
No denying that 3dl Marathon sails are not the choice for a trip to the Caribbean but for the way we use our boat, I can't imagine a better blend of shape vs life.
Bruce