Your options for imaging are to either NetBoot, image via USB like you do right now, or image via Target Disk Mode (Plug each Mac into your Casper Imaging Mac one at a time) which isn't convenient with desktops. That's really about it.

For this case I would make duplicate USB drives and so you can run multiple sessions at the same time.

@adamcodega is correct. I would add, check if these macs have USB3, if so get good thumb drives for speed or possibly use Firewire drives to help the speed.

Last I checked these were really nice to use.

I would not recommend the Kingston DTM30. I have a couple for this purpose (imaging boot keys) but for some odd reason they won't boot all our Macs, must be some sort of controller incompatibility. Will boot my air and one of 3 mini's fine and the occasional iMac.

I'm running these SSD Thunderbolt drives -

http://amzn.com/B00HR1JJTS

@corbin3ci I've been tempted to order one of these. http://eshop.macsales.com/shop/external-drives/OWC/Envoy-Pro-mini

@tcandela Just to add to what the rest have said, AutoCasperNBI can create a OS.dmg for restoring to external media to boot/image macs.

You could also create a second partition on the systems with a minimal OS and Casper tools. That Autorun data scheduled restarts from the 2nd partition, and you can re-image machines as often as you want to, with zero touch.

As for USB keys, just got Silicon Power 64 GB models for a project - pretty happy with them so far:

http://www.amazon.com/Silicon-Power-Jewel-Titanium-SP032GBUF3J80V1T/dp/B00O4VAKY2/ref=sr_1_4?s=pc&ie=UTF8&qid=1429550494&sr=1-4#customerReviews

thanks - i have multi USB drives