i have always been told, and i believe it, that the bigger the strings, the bigger or deeper the tone. i have always believed that that is due to the bigger area that the string(s) cover over the polepieces or blades of the pickups. as far as the tension, i know that when you want to tune down low, go for bigger strings since bigger strings have more tension in them and this will keep them from being too floppy or loose. unless you want to have floppier strings. smaller strings are better suited for higher tunings since there is alot less tension exerted on the guitar. the more mass, the more power that needs to be used to stretch the strings to the desired tuning. i love heavier strings for real low tunings. but, it's all about taste, tone, and hand feel.