Hi Chuckals;
Welcome to the forum.
Not knowing your smoker model or your final configuration after the upgrade; the lowest smoking temperature you will be able to achieve will be the same before you made the upgrade. Just like before, you lowest temperature with the tempco element off, is the same as running a stock Bradley with the 500 watt element off - and that is also very dependent on the ambient weather. With the element on, if you don't have a third party controller and you are using the Bradley controller and sensors, I wouldn't expect it to run any hotter or much hotter at the lowest setting than with the stock 500 watt element. The main difference you will see is how fast your reach the set temperature.