I'm getting 34MB/s read from the DNS off a non-raided Seagate 1TB 7200 rpm 32mb cache drive.
The DNS is set to jumbo frames at 9000
It's connected to a Netgear 8 port gigabit green switch (QoS but is unmanaged). The switch says right on the box that it supports jumbo frame upto 9000
My motherboard is an older ASUS P5W DH which has that original intel 975x chipset with one of the original dual-core chips. This motherboard sports dual ethernet interfaces. They are Marvell Yukon 88E8053's sitting on the PCI-E bus (supposedly). These controllers do support jumbo frames and are set at 9000 to match the switch and the DNS323. They also have flow control, offload and whole host of other configuration options that I have no idea what they do and haven't messed around with too much.
once past my interface, the data is flowing to 2 x SATA-150 WD caviar blacks in RAID-0. Not sure what the specs are but I dont think they are anythign special. My single WD raptor felt as fast as these two blacks in raid-0.
I too originally experienced slow speeds and I set out to fix it. during my trouble shooting, I found I noticed the largest increase in performance when I enabled jumbo frames at 9000 on BOTH dns and ethernet interface. I'd like to note that my router upstream from my switch is also gigabit and each of its 4 LAN ports can be set to jumbo frames at independant rates. It's incredibly important to ensure that when selecting jumbo frames, you set each device at the highest common rate. so, if you have a router that supports jumoframes at 7000 and the dns supports 9000 frames and your pc interface supports 9000, I THINK you should really be setting all devices at 7000. I THINK. Only when I set all my devices at the common rate, did my speeds become consistant. YMMV