1 - Processor scheduling should be set to background services and not Programs. 
 
This is a very important tip and could make a significant difference to how low you can set your samples per buffer for your soundcard. 
 
A lower samples per buffer setting means lower latency, which is better for vsti's and ASIO monitoring (if you use it). 
 
Processor scheduling should be set to background services and not Programs.This has the effect of switching from more frequent and smaller CPU time slices (applications), to less frequent and longer CPU time slices (background services). 
 
This allows the audio application or driver to "hang on" to the CPU for longer without interruption. 
 
In addition, the background services setting also reduces the amount of "priority boost" that foreground window's threads receive. 
 
Start > Settings > Control Panel > System > Advanced > Performance Settings > Advanced Tab > Background Services