Use the following registry entries to toggle between full-speed, non slowed search indexing and default behavior.

Full speed indexing, with no "backoff":

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search\Gathering Manager]
"DisableBackOff"=dword:00000001

Default indexing, with "backoff":

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search\Gathering Manager]
"DisableBackOff"=dword:00000000