The C5 boar is a 5mm shorter knot than the SOC, I believe, which helps control bloom. The C5 boar became a favorite for me last year. Never have tried the SOC boar. Eventually maybe.I'm leaning to the SOC Mistura, it fills a hole in the collection. I thought the SOC boar was a bit too big so got the C5 boar, but the SOC Mistura seems more under control somehow.