Question: 5324 with jumbo frames = 50% NIC utlization?

Hello, I've got a couple of Powerconnect 5324's I'm trying to use for iSCSI connections.  Isolating down to 1 switch with a single NIC, I'm only able to get 50% utlization on the NIC when jumbo frames are enabled against an Equalogic SAN.  If I turn off jumbo frames, I can saturate the NIC at 100% utilization.  I'm using IOMeter to test.

The testing server is a new PowerEdge R710 and I've used both the onboard Bradcom BCM5709C NICs and a 4 Port Intel Gigabit NIC in testing.  In either case, enabling jumbo frames on the switches pegs the nics at 50% utlization.  I have verified jumbo is working with large packet pings and lookinga t the Equalogic SAN to see the iSCSI connection was created with jumbo frames.

I also tested with an el-cheapo $30 ASUS switch from my home network, using 2 ports on it to do jumbo between the PowerEdge and the Equalogic, and I don't see the 50% limit like I do when connected to the 5324. 

On the 5324 I've used the latest firmware and I had an older one on a test bench that had a previous firmware version. Both exhibit the same tendency when using Jumbo.

Has anyone run into this--am I just missing something on the 5324 or is this an insurmountable problem? I don't have another model switch to test with that supports jumbo so at this point I'm getting ready to buy current 5424's against a budget of zero.  I'd like to make sure there isn't something I'm missing before I make my case for additional funding for this project.

Thanks!

- Steve