The DGL-4100 is similar to the more popular DGL-4300 -- you can get an idea of the 4100 by looking at 4300 reviews and ignoring the material on wireless. And BTW, you can often buy the DGL-4300 for around the same price as the DGL-4100 (sometimes even cheaper), which makes the DGL-4300 typically the better buy. You can always turn off the wireless if you don't need it at the moment.
Jumbo frames are overhyped IMO (probably because of historical issues with slower hardware) and often more trouble than they're worth; modern computers with onboard NICs that avoid the PCI bus typically achieve high throughput without having jumbo frame enabled. That said, of course I'd want jumbo frame support where available, at least to evaluate it.
I've measured around 950 Mb/s sustained through a DGL-4300's switch.