In terms of relatively affordable gear that i've owned, the best sound staging/imaging i've experienced was from an older setup with Infinity Renaissance 90's. The Rens were underpowered driven by my Classe Cap-2100 integrated, but still showed their potential with fast, airy mids and highs, excellent stage width (incl: off-axis response), depth and imaging, as well as tight, punchy bass from the 10" Watkins dvc woofers. With a 200w amp, or strong 100w amp like the Coda Model 11, the Rens would have had even deeper bass and opened up more.
Re: test cd's, i'd probably reach for blues albums like Miles Davis "Kind of Blue" (UHQCD), Anne Bisson "Blue Mind" (UHQCD) and Tony Bennett "Playing with my friends", classic rock such as Pink Floyd "Pulse", and some classical music.