When I'm recording I am mindful of both the sonics and the performance; but I will let performance trump sonics in a heartbeat. I need to play the producer role in addition to the engineer one. And part of this is managing the vibe of the session and getting the best from the talent. Yes, its up to the performer to do the performing, but its up to the engineer and producer to make sure that they are not an impediment to getting that performance. I'm not going to interrupt the flow of the session to go on a search for the best preamp. I'd rather get the take and press on; especially if the talent is 'on'. By contrast, if there's a lull in the mood, sometimes you can take advantage of that and lift it by running through your options and finding a more inspiring sound.