I built the 33609, which is similar to the 2254c. I've never used an API 2500, and I haven't finished building a SSL clone, but I have a MixBuzz in the works. I recently compared the Pico compressor to the 33609 (plus a few other compressors) and found that the 33609 provided a noticeable change to the quality of the sound. On acoustic guitar, it brought out the attack, made it harmonically big and warm. The Pico did not do this, but rather, brought the bus together in a warm way, but did not have a noticeable coloring of the sound. So, for use on a mix buss, I would not think the Neve's would often be chosen. More often a transparent compressor, like some of the others you mention.
I will probably post some sound samples from these compressors at some point if you are interested.