For a six day split your best option is probably a Push, Pull, Legs, Rest, Push, Pull, Legs split. This allows you to hit each mucle group twice per week. It also ensures you take maximum advantage of Muscle Protein Synthesis (MPS), this is the mechanism behind muscle growth and repair. MPS peaks at around 48 hours after a workout and returns to base levels at around 72 hours for a natural lifter. Using this workout you will never go longer than 72 hours without working a body part so you can always consider yourself anabolic, given proper nutrition and rest.