With the speakers 4 feet apart, we have fantastic imaging.
I strongly recommend Stereophile Editor's Choice cd. It has a number of very helpful tracks, both test tracks and music. And John Atkinson describes how he recorded all of the music tracks, with descriptions of how they should sound.
Stereophile Editor's Choice - Test CD - Music Direct
The best way to use the music tracks would be to listen to them without knowing how they're supposed to sound, and then read the descriptions, imho.