Union says proposed pay pact not on par with other orchestrasThe San Francisco Symphony's musicians are about to hit a very sour note, threatening to call off their first performance in China next month unless they score a better-sounding contract. In a confidential memo sent out to the symphony's 103 musicians over the weekend and obtained by The Chronicle, the union's negotiating committee said management's proposed pay and benefits package was inferior to those of other leading U.S. orchestras. Not that the musicians are laboring for starvation wages. They earn an average of $112,320 a year, and under management's proposal...