This paper might be helpful
Examples of Cisco Low-Latency Layer 2 Switches
The Cisco Nexus 5000 Series access-layer switch is an example of a low-latency cut-through single-stage fabric implementation that will meet the requirements of all except ultra-low latency applications. The Cisco Nexus 5000 Series uses VOQs to minimize port contention.
http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/white_paper_c11-465436.html
Another platform that meets most low-latency application requirements is the Cisco Catalyst® 4900M Switch, a store-and-forward switch that fits in the data center access and distribution layers. The Cisco Catalyst 4900M uses a shared-memory architecture with an ultra-low-latency ASIC design.
The ingress buffering process that a store-and-forward switch performs provides the flexibility to support any mix of Ethernet speeds, starting with 10 Mbps. For example, handling an incoming frame to a 1-Gbps Ethernet port that needs to be sent out a 10-Gbps interface is a fairly straightforward process. The forwarding process is made easier by the fact that the switch's architecture stores the entire packet.
HTH
