I think Roger typical prefers flat sawn. I live in the high desert north of Los Angeles and we see 100º + in the summers and low 20º to teens in the winter, with extremely dry air. Roger mentioned that he had a piece of quarter sawn and that it might be a good idea on this bass for extra stability, but I still think he prefers the tone of flat sawn.
Apart from looking great, does the roasted treatment contribute to stability, too? Was guessing it takes the moisture content lower before the neck is carved..?