Pre-loading audio buffers - what is reasonable and reliable?

I am converting an audio signal processing application from Win XP to Win 7 (at least). You can imagine it is a sonar application - a signal is generated and sent out, and a related/modified signal is read back in. The application wants exclusive use of the audio hardware, and cannot afford glitches - we don't want to read headlines like "Windows beep causes missile launch".

Looking at the Windows SDK audio samples, the most relevant one to my case is the RenderExclusiveEventDriven example. Outside the audio engine, it prepares 10 seconds of audio to play, which provides it in 10ms chunks to the rendering engine via an IAudioRenderClient object's GetBuffer() and ReleaseBuffer(). It first uses these functions to pre-load a single 10ms chunk of audio, then relies on regular 10ms events to load subsequent chunks.

Hopefully this means there will always be 10-20ms of audio data buffered. How reliable (i.e. glitch-free) should we expect this to be on reasonably modern hardware (less than 18months old)?

Previously, one readily could pre-load at least half a second worth of audio into via the waveXXX() API, so that if Windows got busy elsewhere, audio continuity was less likely to be affected. 500ms seems like a lot safer margin than 10-20ms... but if you want both event-driven and exclusive-mode, the IAudioRenderClient documentation doesn't exactly make it clear if it is or is not possible to pre-load more than a single IAudioRenderClient buffer worth.

Can anyone confirm if more extensive pre-loading is still possible? Is it recommended, discouraged or neither?