If you are worried on a laptop that the USB port is your bottleneck (and it generally is) then consider using some light compression on your images. Quite a few forensic CDs these days will compress your image files for you. I agree with Jonathan that your method is like using a sledgehammer to crack an egg. Network imaging is generally my last resort.
Helix3 Pro initiates iSCSI on boot. You only need to run an iSCSI initiator on your exam machine to connect. You do not need F-Response if Helix is booted on the target machine. This does not apply to the live side of Helix. The last webinar Drew Fahey did at e-Fense was on this very topic. He demonstrated and gave step-by-step directions to connect via iSCSI. If you are a subscriber, it is still there for download. That was also the last webinar that actually provided any type of decent information on practical uses of Helix.
If you do use iSCSI, do not use the Helix3 Pro imaging application on a Windows examination machine to image a logical volume on your Helix booted target. My testing showed that the Helix3 Pro Windows application does not acquire all the sectors of the target logical volume when acquiring over iSCSI. e-Fense / Access Data have confirmed my results but I do not believe that the latest release has fixed this issue.