Not sure I understand your question. A Cisco 3750G switch with a 32Gb fabric can support line rate (bi-directional traffic) on all ports simultaneously. Obviously the theoretical maximum bandwidth through the switch is exactly 50% of the total of its switch ports because traffic is thru a switch, in and out. You can't send traffic in on more than 50% of the ports because the traffic wouldn't have anywhere to go.
All Cisco stackable switches made within the last 7 years or so have supported layer-2 line rate on all ports.
The better question to ask, however, is what is the layer-3 forwarding rate. In some cases, that number (measured in pps or packets per second) can be significantly less than the layer-2 theoretical forwarding rate, particularly with smaller (< 128 byte) packets.
From a slightly different angle, all these numbers change drastically when you 'stack' switches (3750) or cross-connect switches (2960/3560/etc) or use a chassis based solution (4500/6500, depending on supervisor and linecards). The uplinks to a core switch also can have a significant impact on performance.
The rule of thumb for good design is between 8 and 16 to 1 oversubscription at the edge (48 gig copper ports to a 4-port gig uplink bundle), no more than 4 to 1 oversubscription at the distribution layer, and absolutely *ZERO* oversubscription at the core and server farm layers.
I would always recommend you eliminate oversubscription at the distribution layer if at all possible in your design.
Keep in mind that statistically 300 users in an edge switch stack or chassis will not, with high probability, be transmitting or receiving data at line rate at the same time. In the distribution and particularly the core and server farm layers, this is not the same. There is a very high probability that hundreds or thousands of users could be requesting significant bandwidth from several servers simultaneously. This obviously is determined more by the type of industry and types of applications deployed, but is a good general rule.
