Just to explain my post - increasing texture size will increase the amount of detail but when working with older models where PC memory resource was more of an issue the UV map may be stretched to allow all objs in the model to fit on the same texture map. This could lead to less than expected improvements. Attempt at demo of how UV mapping impacts detail below - both images rendered using same obj and image but one of right has a stretched UV map - where the UV grid is narrow the render engine stretches the pixels across a wider section of the obj causing a loss of detail. Stretched UV map shown below also. It should be possible to exploit this to increase detail on parts of the obj where detail is at the expense of areas that are unseen.