I have a sheeva plug. It's been running my home phone system (based on Asterisk) for the last year or so. It was easy to set up and has worked well for me. Several services are running on it, including apache, which serves a webpage i use to get my voicemail. I'm not sure exactly what you mean by 'high performance', but it does the trick for me.

I know you're already aware of it, just thought I'd share my experience.