I've seen some discussion about flash drive installation of Win 7 but no actual metrics and cautions/advice. Here goes...
I installed 7260 X86 on an Inspiron 6000 Laptop (no speed demon) in 17 minutes flat. One word of caution, you have to temporarily remove the flash drive at each re-boot during installation or it will boot to the flash drive and start the process over each time.
Here is a link to the best discussion I have found on creating a bootable flash drive with Win 7