the curve with a volume dip in the middle sucks for a reason noone has mentioned so far (at least I did not read it, maybe I have missed it)
for example:
you doing longer mixes all nite and you are mixing with the channel faders, you have not touched the crossfader for an hour or so, it just stood in the middle
now: you want to make a sharp cut, using the crossfader; the playing record is on channel 1; you have to move the cf to ch1 (and cue the record on ch2); but when you do that, the volume on a mixer with the curve described above will get louder, so you have to adjust the channel faders; if you have a curve without a drop in the middle, you can just turn the cf to the playing channel and prepare the cut