I don't have 6509s so I don't know if yours support netflow commands, but I frequently need the same info. I have 4506 switches with netflow cards, and for real time traffic you can type:

show ip cache flow | include K

and it will display only the lines with kilobytes of traffic so it is easy to pick out the highest L3 traffic.

I think it is much more useful to use snmp to generate graphs. I graph all of my server ports, and all of my trunk ports. Also, if your switch support netflow export, that can be really useful if you have some software to take advantage of it.

The problem with command line is that you can't tell whether a given amount of traffic was all at once or over 10 min. That can make a huge difference. The only bad thing about snmp graphs is that network server backups have a tentency to re-scale the graphs. I have used them several times to track down errant devices. The last time was when our helpdesk guys were multicasting by accident. I tracked it right down to their lab.

Randy