Here is my take on this interesting question. The combination of clay bodies, glazes and firing conditions are endless. On top of that the techniques or combinations that you submit your work to are endless. As a general rule most people bisque at 06-04 however firing a bit lower will give you a "thirstier" bisque that may be better for naked raku or a combination of color slips and underglaze art on a raku vessel. I have been very resistant to test firing due to limited studio time, but I've learned the hard way that testing is key to satisfying results. The more the scientific approach and documentation we do the less the frustrations.