I would say that if you are one of these that rides 10,000 a year then every 6 months is just barley enough. The very basic Jagwire cables that you bike shop has in bulk would only go 3 months before they are corroded. On the cheap you can get them to order you a Jagwire Racer cable kit. Comes with shift and brake cables and you can choose from all different colors. Replace those once a year. With the cheap cables the inner wire isn't stainless steel and will corrode quickly.