Haven't seen or used the W. Bill version. Saying this because of how much I liked the Harrison's camel hair.
Cashmere is durable but wouldn't recommend it for a daily use coat. Client wore one as a daily beater and the nap wore severely on the sleeve openings, front edge of the coat and the along the hem. If the coat is in rotation and worn infrequently it would hold up for years but the pure cashmere will show more signs of aging.
80% wool, 20% cashmere blends have the same surface look and is more stable and a good alternative. You can get patterns, mainly herringbone and a broader range of colors with the 80/20 blend.