IMO You'd be better off with AMD if you want the flexibility. They've been using the same socket for years and just a firmware update to support new processors.
My best attempt at a $500 build (I'm from the UK, its ~£300)
http://pcpartpicker.com/p/2hyKC
mATX so small and transportable (LAN sorted) Should be capable of running Planetside 2 at 30FPS I'm not sure about running everything at Ultra though, you'll have to scale back on your budget or an extra $250 and you can start making demands
If you want to go Nvidia you could swap out for a 650TI Boost but you loose some (fractional) MHz for more moolar http://pcpartpicker.com/part/asus-video-card-gtx650tibdc2oc2gd5boost