For an experienced triathlete with 5+ years of back-ground in the sport and a minimum of 2 1/2 IM done, then 10 hours/week, if it's done right, can yield a decent IM performance. N=1 - I did 9 IM races in my time - all under 10:00 on about 10/week average over the course of a year. Note I said average. Some weeks were much bigger and others smaller. The key is dosing and periodizing the training over the course of the year.
Steve Fleck @stevefleck | Blog
Steve Fleck @stevefleck | Blog