Well I play 4.0 singles on indoor hardcourt during the fall/winter...and the same outdoors in the spring/summer. I don't really break strings, but then again all I use is poly and gut (2 most durable strings on the market). Plus in an 18 x 20 frame...my strings never break hence dropping the gauge all the way down to 18g or less (?).
Interesting, how is that setup working for you? What racquet do you use? I'm mostly a flat hitter with a bit of s&v thrown in. I don't think poly would help me much as I don't have the batspeed or swing trajectory for it. I'm trying the isospeed cross soon at mid tension so hopefully that will reign in the power of the gut. I'm just trying to find the thinnest, most powerful strings to put in this thing while still retaining a good amount of directional control.