You have to look through both to see which you like in low light.
The #4A reticle is the same as the #4, except that the heavy horizontal crosshairs are farther apart (roughly another 25%).
The plex reticle Swarovski now offers is simply the #4 with a heavy top line as well. They used to call this the #7, and also used to offer the #7A, which was the same as the #4, but again with a top line.
The only use I have ever found for the plex was to use as a range finder.
I'm not sure how old you are, but I can tell you that at 54 with 20/20 corrected vision, I really can't use the fine crosshair reticles anymore for hunting in the Canadian Shield bush. They just disappear.