Seems to me there are two issues here - first, people want the best regardless of actual requirement, so the interest in making these comparisons is understandable. However, the real issue is "what problems can you hear with your equipment in actual normal use?" - and I strongly suspect that these days, when recording live music, preamp noise is unlikely to be an issue other than with really cheap and nasty equipment.
I record classical music. When I look at the meters between movements, with levels set so that the loudest parts of the performance will peak to close to 0dB, typically they are flickering around -55dB at best. If I bury the mic under a pile of blankets in a quiet room at night, I might see the meters hover around -85dB. In other words, the ambient noise of a performance space is normally way above the noise floor of the equipment.
So, avoid the few preamps that might be identified by measurement or reputation as significantly worse than the rest, and you'll probably be perfectly happy with the performance of the rest under real world music recording conditions.
Or am I being unrealistically complacent?