I would do two 100w heaters assuming you are running the second as a backup. I have 30 gallon with 20 gallon sump and run a single 150w heater for the last 6 years.
The general guideline for a single heater is about 5W per gallon for a 40g (1x 200W). So with two heaters working to heat a tank UP TO 10 degrees above room temperature, you'd look at getting 2x 100W. I can suggest that Finnex is a good brand. Not sure about Neo. Be sure to get one with a Titanium Body as it acts as a grounding probe as an extra added bonus. Also, pick up a controller as well. And GREAT job with deciding on redundancy.
For heaters I still follow the old 3-5 watts per gallon rule, and I always go for 5 watts. So I would get 200 watts for that tank, with an inkbird controller for safety sake.