My method - YMMV
What I would do
1st I would not even consider doing an upgrade.....It wastes more time than it saves and will probably require support later on which you don't want to have to do.. Unless this is a necessity which isn't mentioned in the article.
Backup up all required files, then install fresh W7 copies..
Sysprep is your friend, the best tutorial I have ever found/used is as follows
DVD or an ISO image , You will need a version of the W7 DVD or an ISO image.... a large bootable USB key, I use 2* 16Gb ...
If your are successfull with the Sysprepping + Testing then each install should take no longer than 1hr each, dependant on the software updates that will undoubetdly be triggered. make sure the PC is "fully" updated before doing the sysprep.
Do "ALL" of your prepping/testing BEFORE you head out..... Do, do the testing.......
Use http://ninite.com/ for downloading/updating those little must have prgrams that we all need/use ( Thanks go to Trevor Potts for the introduction to Ninite)
Just in case Sysprep fucks up the hidden admin account ( This is why testing is vital)
Thats my 2cts worth ( I actually use this method)
Don't know the answer relating to the bandwidth issues