What equipment do you use? heater, lights? That much variance on the west side of Washington is kinda nuts, i could see if you lived in FL. Is your ambient temperature fairly steady? While it may not be causing any problems now it is still early in the summer and you could be getting close to 90 degrees in your tank as the temperature outside rises. I'm more curious about what type of heater and lighting you have though as I'm sure your room temperature isn't anywhere near 84 degrees in Seattle.
When i say consensus, most people will say 78 degrees. Because well it's kinda in the middle, and it works for most people and leaves overhead in-case you do have some temperature fluctuations in the upward direction. While the temperature varies all over the ocean we can't really replicate that pattern and if you did you will most likely make something in your system unhappy so we choose something in the middle that will most likely appease both crowds.