OK, I got my rackets restrung (the elbow is better already, thanks for asking!). Both are AeroPro Drives, Wilson Sensation strings for those who care about such things. One is at 55, one is at 58. I was thinking of using the looser one for mixed for the bigger sweet spot and less vibration for the elbow. Today, I used the looser one in a ladies social match, just to test drive it. I was much surprised to see my serve was noticeably faster. I noticed some difference in groundstrokes too (less topspin, more power). Didn't see much difference in volleys. I was thinking of using the loose racket for my own service games and the tighter one for the other three doubles service games. Is this insane? Do people do this? Or should I just go with the original plan of using the loose one for mixed? Boy, had I known that good strings make such a difference, I wouldn't have waited 14 months to change my strings!!! I'm a believer now.