Well, probably not. Most cable modems (the router), for example, are fitted with 100 megabit, not gigabit ports, so the switch port with the link to the modem will auto-negotiate to 100Mbps, even though the port may be capable of 1000Mbps. A PC with 1GbE connected to a 1GbE switch will indeed run at one gigabit per second on that link, but the connection to the modem will be a bottleneck. Since the switch will use a store and forward strategy through the speed gearing, no data will be lost, even though you probably don't have flow control engaged. And hopefully any multi-frame messages are sent using TCP, so each connection is acknowledged and flow controlled by TCP up at Layer 4, so you don't permanently lose any of them.