> any piece of high quality pro audio gear should idealy have an s/n of -100dB
Why stop there? Ideally we can want more.
Because we have 96dB 16-bit stuff? Well, yesteryear we had 70dB stuff and tomorrow we'll have 120dB stuff, so "100dB" is so "to-day".
> a piece of gear that has been tried and true for a long time.
Since the days when 60dB tape was king. A lot of "great" stuff from that vintage isn't better than 60dB. Notably the LA2 type limiters: input (at grid) noise level around 5 microVolts, 1:50 gain after that. So re:1V we have 20mV/5uV= 72dB noise to reference level.
You know how you like to measure "S/N" but unless you specify conditions it is hard to compare results. In advertising, "S" often means "peak clipping level" and "N" means "heavy weighting filter" because that looks good in the ads. And peak clipping makes sense on digital media. In tape we used 3%THD but whanged the peaks up 10-15dB higher, so "60dB S/N" is really more like 75dB in a digital media. Inaudible power hum can add 20dB to a weighted measurement. When you read "S/N numbers", the conditions are often more important than the number.
And a limiter has a special problem. In varu-Mu (I have not studied VCA in depth) I can get an input range over 100dB. But the whole point of a limiter is to reduce dynamic range. If I expect to take up to 30dB of limiting, then the output dynamic range has to be 70dB. Similar conundrum in FET shunt limiters: an FET will distort over 30mV, for 30dB gain reduction we need 47K series resistance, noise level is at least 3uV, output dynamic range can't be over 80dB.
Noise levels in BJT VCAs are very funny. They've been trying to sort this out for 30 years. Many designs have excess noise around unity-gain, where both sides conduct, though they may be relatively quiet at high gain or low gain. Unfortunately that is where you idle a limiter.