I would take two PC-2000s over a single PC12-Plus in a heartbeat. The Plus series of subs are getting pretty long in the tooth, they are SVS's oldest sub at the moment. My guess is they probably don't have a huge advantage over the PC-2000s, maybe mostly only at frequencies below 25 Hz. Above that, I would guess maybe only a 2 dB or so advantage, if that. Keep in mind this is all speculation. For sure knowledge, ask SVS.
I am also guessing that SVS will revamp the Plus platform within the next year to bring their new amplifier technology from the 16-Ultras and 4000s to the Plus series. They will probably rename the Plus series the '3000' series, since that fills the gap between the 2000s and 4000s. SVS may take that opportunity to enhance the driver and get more performance out of it.