ive got some ce4's but they have different coils in so not sure on what you have.
the easiest way is to turn it up and try it. the worst it can do is burn the coil out and you will have to replace it and you then know best kept at the lower wattage/voltage setting.
As mrdj said the coil a do vary in the ce 4 clearomisers but more often than not it's an aspire bvc or similar. As I stated previously 3.7v is the usual running voltage. Lower will give you less vapour, a cooler vape and probably elongate your coil life. Higher will give a warm intense vale but kill off your coils quicker. Top voltage will blow or burn your coil pretty quickly.Thank you for your information.