Have you ever appended the /SOS (or, /bootlog) switch to your Windows OS bootup line inside boot.ini in root of C:\?
IIRC, that /SOS switch will show you (ala oldstyle OS loaders, like Linux has/had) more than just the "dots" of the drivers loading (like NT 3.5x & 4.x had showing during bootstrap in realmode), but actually each driver loading.
The /bootlog one is just what it says - it logs things during bootup & progressions of it. This switch turns on boot logging to a file that is named systemroot\Ntbtlog.txt.
That alone MAY help you diagnose which driver is "hanging up" or loading slowly, so you could look for an update or alternate (or. possibly report this to its vendor).
Another possible that MAY help you, is the user of the "Driver Verifier" tool, verifier.exe... did a post on how to use it here @ these forums:
http://forums.techpowerup.com/showthread.php?t=12810
* Hope that helps, because I am assuming its driver related, (could be a service too though) because of what you're stating...
However, I could be wrong, just like anyone else (assuming is dangerous, & I am not "right there" & all that, only 'remotely debugging' you here as are others).
There is also a "VERBOSE SWITCH" during your logon that MIGHT be of assist to you, & it's done via a registry hack (reports what's going on more specifically during logon for you), here are its particulars:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system]
"VerboseStatus"=dword:00000001
(Watch that space that's appearing in the word CURRENT in that path in the registry - for some reason? On edit here, it's NOT showing a space, but it IS on posting... don't "cut & paste" that, manually enter it is my advice)
APK
P.S.=> Now, if it's NOT drivers? I would suspect services... only way to really diagnose that imo, is to "trial & error" it, enabling only a minimum set & then enabling others (there's a decent set of guides on this forum for services trimming if your not "into" that yourself, but odds are, you are!)... apk