network card bandwidth on a poweredge 1850?

[Brett Dikeman]

I'm testing a backup server (Legato) on a Poweredge 1850, running Centos 5.2.

I saturated a single gigabit connection, and switched over to a pair
of bonded ports.  Unfortunately, the throughoutput I'm seeing is
virtually identical- 980Mbit/sec according to Munin stats (on a single
port, the limit was 975.)  Half a percent seems statistically
insignificant.
-I should be feeding it plenty; I have 10 simultaneous sessions from a
collection of machines, several of which can do 40MB/sec on their own.
 A survey of the machines shows none of them working very hard.
-The switch is no slouch; a lightly loaded Cisco 4506.  Everything is
on the same blade.  Traffic is not crossing any subnets/VLANs.
-The backup library is about as fast as you can get; 2 LTO4 drives,
each on dedicated FC, into the machine's 133mhz PCI-X slot.  Each
drive has been proven to independently work at over 100MB/sec.
-Seems to be plenty of free CPU time; 25% system, 25% nice (legato), 50% idle.

My main suspect was the onboard NICs, but according to lspci, they're
PCI-X devices operating at 133mhz.  That's...plenty!  1024MB/sec or
so...

I will be running more tests to eliminate each piece of the puzzle,
but- has anyone managed to get more than 1Gbit/sec out of an 1850
using the onboard NICs?  Or, alternatively, tried but found it
impossible to do so?  Unfortunately, I do not have any spare NICs
hanging around at the moment, otherwise that would be a very painless
test.

Thanks!
Brett