You may be better served posting these questions on an EU-based forum, as this place is geared towards the North American market. Model lineups and branding vary heavily from region to region. For example, Panasonic's 2013 NA lineup, from worst to best, went X60-S60-ST60-VT60-ZT60. There was no GT model for 2013 here. Other series (ET, DT, WT) are used for LED models and not plasmas. They also do not use the Prime and Next designations in their marketing here, but Reference is reserved for their best models. My best advice is get one while you can if they are still available in your region, as there will be no new plasmas from Panasonic for 2014 or beyond.
ht Panasonic 60" ZT60, Monitor Audio: Silver RX6, RX Centre, RX1; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D, Panamax M-5100PM
2ch Sony 32" W650A, Sonus faber Toy Monitor, REL T3, Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Apple TV, Peachtree Audio DAC•iT, Panamax MR4300
pc Monitor Audio Radius 90HD, Audioengine D1, FiiO A1
+ Sony 65" XBRX850B, Sony BDP-S5100