I would do far more research than one helpful guide (aqadvisor) and one place that sells fish (liveaquaria). Sometimes the scientific papers that describe the fish can give you an idea of the conditions a fish lives in in the wild.
One fish mentioned here on the forum lately is the 'white cloud minnow.' It is often sold as a tropical fish, but is more accurately considered a cool water fish. It is found in streams that range from the 50s to the 90s, depending on the season. Keeping them in that range would be 'correct,' so a tropical tank in the high 70s is not out of their comfort zone, nor would keeping them in a goldfish tank in the 60s.
Most fish are very adapable and can tolorate a wide range of temperature. Many of those commonly sold in fish stores are captive-bred in large facilities in Asia and the southern USA where they often do not provide them with the same parameters as the wild-caught fish live in.
Unless you are trying to breed specific fish or keep very sensitive fish, I wouldn't worry too much on providing an 'ideal' temperature. Stability is best for most fish.
Just my 2cents.
OC