Thanks. I believe the problem was loading the file from a network drive. Don't know why that would matter but opening large mp3 files saved to my local disc processes quickly as they should.
I'm having the same problem. A 30 minute 128k/b mp3 file is 27.8MB in size and takes 5 seconds to open in Aud CC, the same file takes over 25 minutes to open in Wavpad. Any ideas?