You may not appriciate my nosing into this since I'm a lowly guest and should probably set on the back pew and keep my mouth shut--but:new strings,regardless of guage are going to sound different than old strings--generally speaking they may be brighter, and louder, and with regard to the old strings, you have probably become accustomed to them and their tone. Some wound strings ,even though they are the same guage, are made up of different metal alloys, which would make them sound different too. I think you were wise in choosing the lightest guage first. It also seems that this might be a one time issue for you because after you have replaced that first set, you are going to know what guage you have.You may have to go thru a set of medimum's first before you are pleased. If you are intent on a string guage,I have seen piano technicians with a "V" shaped string guage--you might try your local piano tuner.You didn't mention the manufacturer or your reso, but you might inquire to them as to the brand/guage of string they place on their instruments. I'll take my seat now...thanks