“It is an illusion that photos are made with the camera… they are made with the eye, heart and head.”
— Henri Cartier-Bresson
My advice is going with the first model. The heftier graphics card will do more for your video playback than the fusion drive. Plus you'll have USB 3.0 and thunderbolt which make firewire seem like cruel and unusual punishment. And you can upgrade your ram by yourself, which is as simple as popping in the back of the imac. I just got a new 2013 imac and it absolutely shreds through footage on Premiere Pro and FCPX. And since you mentioned that FCPx is your choice program I really recc. the 1st imac. The newer processors with mavericks OSx are made to work really well with Final Cut Pro 10. Like calvin said, if you can splurge for an upgraded Hard Drive that is solid state (SSD) you'll really be sitting pretty.