Speed we have, approx same as you have quoted for fat client logon 15-25 secs new profile cached profile 5-10secs.
Management of software we have can deploy software at the click of a button and have it installed immediately on the fat client workstation (knowing that it will run).
Power usage is slightly more per machine for our fat clients than thin (looking at ways to reduce this).
Storage and connectivity includes remote access from anywhere in the world (Cloud computing) and when we move onto our next platform we hope to move into the virtual desktop environment with Citrix which will allow our users access to their desktops anywhere and use all the software that the school resources has.We have bought and maintain our own SANs plus our whole infrastructure and have done for the past 9 years.
Obviously we have not spent the earth on our system but we have managed it well and the Infrastructure is there which is the key point in any good network whether it is LAN or WAN.
Why would we want a thin client architecture throughout the school if it doesn't deliver what we have now at even more expense to the school to fill the coffers of corporate businesses pushing totally new concepts for their own profits.
I don't want to seem against new concepts but when companies state one thing and they mean another then the confusion they cause along with the interruptions to the students teaching and learning has an impact on the schools involved, and all in the name of progress.
I don't doubt for one minute that your clients are as happy as can be with the solutions you have provided for them but what is the benchmark you use as the measurement of your success how have you measured it?