First, I would agree with Randy, switch to 20/50. Any good brand, I use valvoline. Running at higher RPMs will increase consumption, but a quart in week seems too much. How far do you drive in a week, how much time at high speeds? Before you decide you are not leaking, consider that at highway speeds, a leaking oil pressure sender or oil thermostat o-ring can drip fairly steadily, but the oil blows away and does not leave any evidence. Examine this area closely.