After a mere two rehearsals last weekend, the Quad City Symphony Orchestra (QCSO) treated roughly 7,000 audience members to a smart, polished Holiday Pops concert Saturday at The Mark. Joining the QCSO’s 82 musicians were 109 singers from the Davenport First Presbyterian Church Sanctuary Choir, a 97-voice children’s chorus, 22 members of the Figure Skating Club of the Quad Cities, and jazz quintet The Hot Club of San Francisco – a rather grand total of 315 performers.