1280 x 960 is my standard export preference, but I try to remember how big the texture will end up in the final render. When you put loads of parts in one texture map, the definition of individual details can be lost. When it is just the rearview mirror ( in which things may appear closer than they are, as Meatloaf observed so beautiful ), you do not need that much information. The fun with UV Maps is, that if you scale down the whole thing, the relative placement of the pixels stays in place. I.e. if you scale down to a half, that 'Penzoil' decal still will be in the same place, when you re-open the file in Carrara. The practical part is that it keeps your file lighter and the render a bit faster. Half the time things I make are meant to be printed professionally (dimension as in print, resolution 300 dpi), so the texture maps that are really close should contain enough pixel information to hold up to that. The car is looking rather Fast&Furious already! Try to insert a 'plane' primitive to get some shadow (contact with the ground), that helps to 'feel' the mass of the car. Good luck! Keep rendering.