I would add two more Randy---violin and cymbal, to test a systems ability at high frequency timbre. Piano and snare drum also tell you about that, but not to the same degree. Getting the ping/click of a drumstick tip on a cymbal right, and the sheen of violin string overtones, is very telling of the behavior of tweeters, pickups, and amplifier circuits. To get the combination of detail and sweetness, without etching and/or hardness, is a tricky balancing act.