Using a couple assumptions on your evaporation rate, heat contribution from pumps, and external insulation, I calculate that you have an ambient room temperature of 70 degrees or lower. (This is an estimate, but I didn't give you much heat contribution, so if that's a lot more than 50 watts, you may have a lot of excess evaporation or an even lower room temperature.)
To get the tank temp to 89 F, using the same assumptions from above, you're going to need 788 watts of heating. For 87 F, you will need 703 watts.
You can of course reduce that if you can reduce evaporation or add some insulation. And of course, whatever the room temperature is, by raising it, you can reduce your heating requirements as well.
Every 1 F you raise the room temperature, will drop the heating requirements by 40 watts.
As a result, raising the room temperature by 2 F, and lowering your target to 87 F, will drop your heating needs to 621 watts.
If it were me, I'd first try to reduce evaporation or add some insulation. Air drafts around the tank will remove heat, as will water escaping from the tank. After that, I'd decide on my target tank temp, and then, allowing for whatever I wanted to do with my room temp, I'd purchase accordingly.
Of course, in the summer, it could be that the room will be warmer. But in my model, to hit 89, you're still going to need around 600 watts in a 75 degree room.