Yeah, thanks, hard.wav is a killer for joint-stereo! I turned off joint-stereo and now 320 kbps is almost as good as 512 kbps was with joint-stereo on. I'll put up a new beta with an option to turn off joint-stereo (it's already supported in the format, there's just no switch for it).
I found another difficult file that is actually from a real CD. It's from the Fast and Furious (copy-protected) soundtrack and I posted a clip here:
ftp://syv.com/david/furious.wv
The second electronic noise bleep has many HF spikes that introduce audible noise below 448 kbps. Turning off joint-stereo doesn't help this one (it hurts, in fact) but I have an improved (but slower) decorrelator that does help significantly. I am trying to get this in as a "-h" option in the near future.
However, I still believe that for the vast majority of real music the compressor is transparent at 320 kbps. The intent is to provide lossless compression with a free bonus of a high-quality playable file of reasonable size. There's no way that WavPack's lossy mode can compete with perceptual codecs at low bitrates (except maybe on those test samples that sub-band coding has trouble with).
Thanks again for the input.