Thank you! I've never had to RMA a motor from you before, so I didn't know how involved the process would be. Should I use the address on your website as the return address for the armature I suspect as defective?
Motors aren't really limited to specific voltage ranges, they're just rated that way for warranty reasons. You can run any modern RC motor on 4S, you just have to be careful to use it in a situation where it won't stall and cause the battery to shove tons of amps through it. Part of it is selecting a higher-turn motor than what you'd use in the same vehicle at lower voltage, because a higher-turn motor will have more electrical resistance to limit the amps the battery can shove through it. The other part of it is gearing the motor to ensure it can get the vehicle up to your target speed -- and no higher. Higher-than-necessary gearing keeps the motor in low RPMs longer; motors have lower electrical resistance at low RPMs (lowest at 0 RPM and steadily rising until they hit top speed), so the battery will shove the most amps through the motor at low RPM, increasing the risk of overheating.
The exact balance of higher-turns vs. lower-gearing depends on the acceleration you want vs. the battery life you want. If you want faster acceleration up to a given top speed, you need a lower-turn/higher-RPM motor with lower gearing; on the other hand, a higher-turn motor with higher gearing will reach the same top speed at a lower overall rate of power consumption, with the tradeoff of slower acceleration when you hit the throttle.
If you want to stick with a 550-size motor (which is my preference for something as big and fast as a SCT), on 4S the 21-turn TMP550 should give you more than enough speed. If you want to err on the side of safety, you could get the 30-turn limited edition one and gear it higher.