Chicken Breast goes through a variety of textures as the temperature rises. In the low 160*'s it is " Done " but will be slightly pink, very juicy, with a somewhat rubbery, dense texture. In the high 160*'s the meat whitens, get's firmer, is still quite juicy and the muscle fibers barely begin to seperate. In the 170*'s the meat is very white, the fibers can seperate into strips like string cheese and the meat begins to get dry. In the 180*'s the muscle shreads like pulled pork , is white and quite dry. Bottom line is... a few Degrees of Internal Temp, one way or another, gives a very different Texture in the meat.
Yes there are some other factors... If you are going to the Grocery and the Boneless Breasts are in the 12oz range, size of a large man's hand, that is an Old bird or ex-Layer and will be much tougher and more Rubbery than a 6-8oz Breast from a young 3lb Bird. You need to choose Chicken according to cooking method. Big 8Lb Chix, Oven Stuffers, are good for Roasting/ Low and Slow Smoking and moist cooking methods, Soups/Stews/Braised Dishes. For Frying/Broiling, 300*F Smoking and Grilling, small whole birds, 3Lbs, and smaller parts are a better choice and will be more tender and have a better texture with these quicker cooking methods. With all Birds...Brine 4-24 hours for Tender, Flavorful, and virtually guaranteed Juicy Poultry... Hope this adds some insight...JJ