two problems that effects speed (that I have incountered) is if the kixtart files are on the local machine and what DC you are authinticating to. If the DC is far aware see this technet article to balance net load Q167029. And add this to your script to copy the files to your local machines.

If @INWIN=1
If NOT Exist ("c:\winNT\kix32.exe") Copy @lserver+"\netlogon\kix32.exe" "c:\winNT" EndIf
If NOT Exist ("c:\winNT\kxrpc.exe") Copy @lserver+"\netlogon\kxrpc.exe" "c:\winNT" EndIf
If NOT Exist ("c:\winNT\system32\kx16.dll") Copy @lserver+"\netlogon\kx16.dll" "c:\windows\system32" EndIf
If NOT Exist ("c:\winNT\system32\kx32.dll") Copy @lserver+"\netlogon\kx32.dll" "c:\windows\system32" EndIf
If NOT Exist ("c:\winNT\system32\kx95.dll") Copy @lserver+"\netlogon\kx95.dll" "c:\windows\system32" EndIf
EndIf

If @INWIN=2
If NOT Exist ("c:\windows\kix32.exe") Copy @lserver+"\netlogon\kix32.exe" "c:\windows\kix32.exe"EndIf
If NOT Exist ("c:\windows\kxrpc.exe") Copy @lserver+"\netlogon\kxrpc.exe" "c:\windows" EndIf
If NOT Exist ("c:\windows\system\kx16.dll") Copy @lserver+"\netlogon\kx16.dll" "c:\windows\system" EndIf
If NOT Exist ("c:\windows\system\kx32.dll") Copy @lserver+"\netlogon\kx32.dll" "c:\windows\system" EndIf
If NOT Exist ("c:\windows\system\kx95.dll") Copy @lserver+"\netlogon\kx95.dll" "c:\windows\system" EndIf
EndIf