I need to buy a back-up KBT. Assume that I get both of those racquet strung on the same day, same string, same tension, all the specs are the same. How do I go about using those two racquets to maintain their playing qualities as close to each other as possible? Do I play with KBT #1 until the strings break, and only then switch to KBT #2? Do I try to keep the playing hours about the same with each racquet? How should I go about this? Thanks.