when uplink utilization exceeds 50Mbps with 10k packets per seconds, users start to complain about slow network performance. while monitoring uplinks, switch performance, packet discards always zero, 0 collision frames, 0 runts, 0 output errors, and all servers perfromance are normal.
This behaviour is to be expected. Cisco Catalyst range of switches, which includes the 3750/G/E/X and the 2960/G/S/X, were never (ever) designed to connect to high-speed servers. When you connect servers to them, because the Catalyst switches have low memory buffers, you'll start seeing packet drops. It is OK to connect 2960 to iLO or DRAK cards, but the main distribution ports is not suffice.
Cisco's Nexus solution addresses the requirements to connect servers, iSCSI, SAN, etc at high speed, low latency, hitless scenario.