Acceptable Domain Logon Times?

I am an IT manager at a school (800 users in total). I have only recently taken over, and we have migrated to Windows 7 (also upgraded the domain to Windows 2008 R2). The school employs a rather expensive IT consultant (friend of the Bursar), who is constantly on my case, as i literally ripped his solution apart (RM if anyone knows that name?) as I convinced the school to move to a more standard / corporate solution for the IT.This consultant is stating that the performance (logon times) are slow, and i wanted some feedback on the people on here.

In a nutshell,

- Windows 7 desktops (32 bit, Professional)

- Windows 2008 R2 domain.

- GPO used obviously for locking down the OS - though a low number of GPO's

- GPP used for mapping of drives (students get 2 drives, staff up to 6 depending on role)

- GPP used for mapping printers (30 printers onsite, but never more than 3 printers mapped per user session)

On average it takes approx 25 seconds from log on to the desktop.I've always though that if the log on time was below 30 seconds in the above environment then that was acceptable? Not blistering, but certainly not "slow"?