I've tried a couple 18 gauge (118-120mm) setups in my Yonex Ti-70 frames. I wanted to see if it would improve spin potential of the tight 18x20 pattern. My standard setup for this frame is BDE Performance 17 (122mm. gut) mains/ Gosen OG Super Micro 17 (also 122 mm.) crosses at around 55 lbs. While this is a 17 gauge setup, both the BDE and the Gosen are on the thin side for 17, really a 17L, so I was not expecting a drastic difference. The 18g. setups I used to compare were : 1. Klip Legend 18 (120 mm.) mains/ Gosen OG Micro 18 crosses @ 55 lbs. : There was a significant increase in power and loss of control compared to my normal BDE 17 hybrid at the same tension. I was surprised given the difference of only about 2 mm. in thickness. Could it be that Klip gut is just more powerful than BDE? Actually, to be honest, I'm not sure if there was acutally an increase in power, but balls were flying on me more than normal. This frame offers pinpoint control normally with my BDE 17 setup, and with the Klip hybrid, given the same swings, the ball just seemed to be going long. I've heard conflicting things about whether 18 g. is more powerful than 17 g., but thus far in my experimenting with string setups, I have to say that there always seems to be a decrease in control for me when going to thinner gauges. I don't know if this is a power issue, a sweetspot issue, or a ball trajectory issue (it's been suggested that lower string tensions lead to higher ball trajectories, not necessarily greater power). Additionally, either the sweetspot shrank going to the Klip 18g., or the overall sensation at contact was just less solid and stable feeling in general. Possibly just the feeling of less string touching the ball? In any case, this setup didn't work for me, and at best I will try it again at a higher tension, perhaps 2-4 lbs. higher, to see if it's any better. 2. Volkl Power Fiber II 18g. (120 mm.) @ 57 lbs. - This setup had a noticeable decrease in power compared to my normal BDE 17 hybrid, which I expected, given the increase in tension and the move to a multifilament synthetic. I increased my normal tension by 2 lbs. in this case to account for the tension drop associated with multis compared to natural gut. Surprisingly, the stringjob does not appear to have lost much tension at all, even after a couple of weeks of use. I guess you can add Volkl Power Fiber II to the short list of multis that actually hold their tension very well, on par with the Laserfibres, and Yonexes. This string felt identical to Klip Excellerator, and I suspect it is the same considering the 2 companies affiliation with each other. It has very good control and decent bite, and above average feel for a multi. I'd say it plays on the stiff side, but this may have to do with the excellent tension maintenance. There was again the feeling of decreased solidness, or maybe a shrinking of sweetspot, as with the Klip Legend 18 hybrid. The spin potential was about the same as my BDE 17 hybrid, although it is not a fair comparison given that it is not gut (I seem to get more spin with gut than any other string). The power level was quite a bit lower; I think I'd have to string this stuff at 2-3lbs. BELOW my normal BDE hybrid tension to get a similar power level. In any case, the Volkl string was solid across the board, desipte not being excellent in any one area, so I may use it in my "damp weather" frame, when it is too wet to use gut strings. In conclusion, as of now, I prefer the BDE Performance 17 hybrid over anything else in my Yonex Ti-70's, and will probably stick with it as my standard setup. If I get around to it, I may give the Klip Legend 18 hybrid another shot at higher tensions, but I suspect that I may just not like the feel of strings that are 120 mm. or thinner, even in a tight 18x20 pattern. The only possible advantage would be an increase in spin potential, but the BDE 17 is already only 122mm., so I have a feeling the difference would be minimal if at all. I'd love to hear what others have to say on this matter though, of thinner strings either shrinking the sweetspot or making the hit feel less solid, as well as the question of whether there is necessarily an increase in power going to the thinner gauge of the same string.