I think heaters are the weak point in all the equipment we use on our tanks.
So any improvement we try to do with them hopefully will pay off in the long run.
On a tank bigger than 65-75 gallons I would definitely use 2 heaters and I would use a heaters that had a controller.
When a heater fails, it usually sticks on & cooks the tank. I only have a 300 watt heater on a 240 gallon tank with a 100 gallon sump. It does just fine. Room temperature & heat from pumps & lights make a big difference on the size of heater required. A heater controller will prevent a stuck heater from cooking your tank.
I have an apex aquacontroller to protect me from cooking the tank. It sounds like two heaters isn't a bad idea. At least if one goes down, the tank will probably just run cooler and then hopefully I catch it before it's too late.