My son has been playing Klip Legend 17 ga. gut in the mains and Pro Hurricane Tour 17 ga. poly in the crosses of his original Babolat Pure Storm Teams for more than 7 years. I started putting gut mains in for him after he developed tendinitis in his rotator cuff. He has had much success over the years in USTA, high school, and now at an NAIA college using this combo. He does not hit with the extreme topspin you see a lot of juniors exhibiting today, so he doesn't need or benefit from poly mains. (In fact when we've tried switching to poly mains and gut crosses, it was such a difference that he hated it.) He gets a lot of controllable power with the ability to uncork winners from the baseline on-demand. Also gives him additional touch when needed for drop-shots and net play. It has worked so well for him that my daughter switched from a full bed of NXT to Klip 17/Solinco Outlast 17 for the last two years of her college career. I've even used it a few times myself. I am prone to TE and the gut mains really help with comfort. I have found that the characteristics of the mains determine in large-part how the stringbed will play, and nothing plays quite like gut. Personally, I believe that unless you have money to burn, you are not maximizing the playing characterstics of gut by putting it into just the crosses. Four of the features of hybridding this way are 1) You get gut playability but split your cost between two racquets/two stringings. 2) Gut holds its tension a lot longer, so it helps extend the life of the overall stringbed/poly. 3) Gut is very durable, and my experience is that it lasts longer than a lot of synthetics/multis I've tried. 4) You don't have to weave the gut when it is in the mains. Two examples: My son can hit the ball as hard as anyone I know. He is not a big string breaker, yet when he does break a string it is almost always the poly, not the gut. (Remember, he is a flatter hitter.) Also, my daughter used to break the NXT within a week of playing. Since she switched to the gut/poly combo, she has not broken a single string. Both of my kids occasionally have their coaches cut out the bed and restring to keep things fresh. In my daughter's case, while the initial cost of the gut is higher the fact that she is not breaking it means an overall lower cost for the school than the NXT she was previously going through.
All that to say, I recommend Gut Mains/Poly Crosses. (For both of my kids I drop the poly tension by 4 lbs.)
But for we mere mortals I've found that gut/poly provides such casually accessible spin that one can generate it with ease, sort of like how "modern" stiff frames with large heads provide more power with less mass.
