i keep it simple and just use 1 1/2 for all injections, i just don't insert all the way if i inject into my shoulder or thighs. but i use the whole size for my gluts. try to simplify your life.
for the glutes i would definetly use 1.5" ..the last time i used 1" i had a lump on my ass the size of a golfball for a few days..and i dont even have that big of an ass...lol