This is true only if the Racing T crankset OP will "probably be using" can be used with either of 111 or 115, and OP ultimately decides to use that crankset. So if in fact proper chainline with Racing T cranks can be achieved with either 111m or 115mm (I dont have specs handy), then OP should chose 111mm given the 28.6 seat tube. However, he should make final decision about what cranks he plans to use before deciding what BB to buy and check for certain what crankset manufacturer recommends for spindle length.