(E in) is a 'figure of merit' for an amplifier which may help clarify the situation.
The 'equivalent input noise (E in)' is as though you had a noiseless amplifier but with a noise level Ein applied to the input.
Most?? 'pro' mixers feature a mic preamp topology which has increased Ein at lower gain settings.
An example might be Ein -110dB at 10dB gain and Ein -130dB at 60dB gain.
With the above example, the amplifier's output noise (after gain) would be -100dB and -70dB respectively, but if a signal of say -50dB were also applied then the signal output would be -40dB and +10dB which would in turn equate to signal to noise ratios of 60dB and 80dB.
So, from a purely noise performance perspective, higher preamp gain is desirable, but as with most things, there are tradeoffs.
For every 1dB of gain, the input dynamic range is reduced by 1dB. Low level input signals have less noise pickup immunity in cabling for example. High level signals may be approaching distortion from their own output stage. Who knows?
As far as receiving wireless Rx inputs, generally the whole TX/RX system noise is greater than that of even a modest performance mixer front end and so mic or line level input I think is simply whatever takes your fancy.
As an aside, mixer 'Line Inputs' are often simple resistive attenuators in front of the mic level amplifier.
Rob
You're right Jason, the collet type is much easier to assemble although it does require a thin spanner to hold the body while tightening. As an aside, the set screw version contacts are silver finished and the collet version are gold finished. From experience it seems that silver is the preferred choice for dc connectors / switches etc. as it withstands better the slight arcing involved when connecting to 'switched on' equipment. Rob