I don't keep up with them too much but I remember back before the VX300U came out, this place was going crazy over it, and after it came out.....the thread died real quick. I think the general consensus is that unless you really want the industrial-looking bezel, need to swap out input boards, or need the 85"+ model, the pro series Panasonics no longer exceed the consumer models in picture quality. The VX300 was also a late 2011 model, and I doubt it's better than the 2012 flagship VT50, or the upcoming ZT60.
I'd wait for the ZT60.
ht Panasonic 60" ZT60, Monitor Audio: Silver RX6, RX Centre, Radius 90HD; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D
2ch Sony KDL-32W650A, Sony BDP-S1000ES, Marantz PM8004, JVC T-X3 tuner, Monitor Audio Silver RX1, REL T3, Apple TV, Peachtree Audio DAC•iT, Sennheiser HD598
lr Panasonic 50" ST60, Sony BDP-S5100, Apple TV
pc Energy CB-5, Audioengine D1, FiiO A1