I would stick with 180 as long as your car is SC'ed....helps keep the air temp lower internally if only by a little bit as long as the fans are programmed to compensate for the new, lower thermo temp, but 160 is too cold. Most people drill them so that the motor isnt as shocked by being dumped on by the coolant when the thermo opens for the first time. If you drill it it will have a small trickle of coolant to compensate somewhat for this....IMO it is up to you, I personally do not have mine drilled.
