SBS 2003 Network - Broadband Performance

I am having a little spat with a cable tech that told my customer that my
server was slowing down the connection. While not a network guy I do under
stand through put numbers.

The office has 10 PC's, storage PC, and SBS 2003 (Dell 2.3gz 2 mb mem)
A dell power connect 2216 switch (10/100 Base T ports)
Then a DLINK Firewall router/switch (10/100 Base T ports)
Then the cable modem

They say I should get 384 Kbps upload & 6144 Kbps download

When I run a cable speed test (dslreports.com) I get 353 kbps upload and
3550 kbps. (I get the same at my home with a DLINK router)

My contention is that the server running a about 10% usage with 10/100/1000
networkcards on the PC, and the 10/100 devices can still push data faster
then the cable modem pipe can handle.

Any thoughts?