That depends on a lot of different things....
-the temp of your house
-the height of the basking spot
-the heights of your bulbs
-the type of dome you have for your bulbs
-the brand of bulb you use
It's the type of thing you need to experiment with and find out for yourself. I have never used a 40g breeder so I hope someone can give you a little better advice than I can. It's all about experimenting to get the right heat gradient. You will need a digital thermometer with a probe or a temp gun to make sure you're getting the right temperatures. From then on, it's all up to you to find the right distances to get the right temperatures. Hope this helps a little , although I hope someone that actually uses a 40g breeder will speak up.
I use a 100W house bulb for my 20gallon basking spot/hot side but I have heard of people using a 60W bulb to get the same temps for their 20gallon. It's a little of trial and error.