Hi,
we are in the same situation. Locations all over the world and slow internet connections.
I create master images here in germany and image them with Landesk imaging tool.
This images are deployed into every location with DFS (over night).
Deployment with DFS takes ~ 1-2 Days (nights)
An office in US starts the PC with Landesk USB stick or PXE (PXE Proxy installed on a normal PC or Laptop) and
then i am able to deploy the image to a PC or Laptop using Landesk Image deployment, HII, .....
Our Masterimage includes all standard applications so a complete installation takes round about 20 Minutes.
I hope i could help ;-)
Robert