your steering knuckles are what limit the throw on your steering rack. there is only so far it will go. to proper set it, put the car on the ground and adjust the travel by starting at a low number (in your case, 100) and continue to increase the throw until the wheel stops turning. you want to be at the point at which the wheel just stops turning. Don't worry too much about the noise it makes as long as you are setting your throw to the point at which the steering knuckle just touches the c-hub. do this again for the other side.
I say to put it on the ground because there is natural resistance the tires will make. the servo should struggle a little bit to ensure it is putting enough tension on the wheels. IF you set it and the servo isn't straining A LITTLE BIT, when you head out to the track or backyard, your throw won't be from full left to full right. the servo simply won't push hard enough to compensate for the strain of normal driving.
Now if you simply leave your setting at 150 and you really only need 120 on the left and 135 on the right (never have i had a servo perfect symmetrical), you are over working your servo and will most likely burn it up. I don't know of an rc that isn't strong enough to handle the stress of a servo, so don't worry about that so much.