Great that you have given the T-Rex feathers as the evidence is too strong to ignore. And as a rule of thumb, if we do not know whether a Theropod has feathers or not, we always should assume it did have feathers as feathers have been found in almost all Theropod group; in other words, most Theropods are now known (I am sick of saying thought, it is a scientific fact now) to have feathers.
I for one think that feathered Theropods are far more beautiful and fantastic than those silly big lizards that they got depicted as. The truth is that are are fundamentally birdlike, feathered and endothermic, except most cannot fly (other than birds and maybe things like microraptors) and they usually have teeth (except for the likes of birds and ovirirapatorids) rather than a beak. If people saw them they'd think them weird, often massive, birds.
Incidentally they have found a complete specimen of Tyrannosaurid that is almost as big as a T-Rex called a Yutyrannus. It certainly had feathers on at least many parts of its body, and probably completely covered it. With more large Theropods being found with feathers, it is now more likely that T-Rex adults were feathered in at least many regions of the body.