PCQ Errors and Dropped Packets

I have been getting complaints from my client about speed issues. There are typical over 1000 active users that I share the BW across 3 100x10 modems. I have very basic PCQ in place which I am sure is no longer enough for this growing customer. I have noticed huge amounts of dropped packets in the Q statistics. I have looked over the QOS Best Practices but can seem to get two and two together. I dont think I get the PCQ Queue Size limit and total limit. On a site with over 1000 active users what would someone recommend?