my two cents...i havent read or posted in a few months, mainly because ive been too busy and was tired of all the negatively.
i was nervous about my 5d3 purchase, like you are with your 1D purchase. mainly because i mostly shoot with an epic or an alexa, but more and more id get a treatment and it starts off with "this is a 5D job"
so i finally got one, looking back on the past few moths im so happy i did. the entire pkg has already paid for itself, financially and creatively. i shoot mainly commercials, and more recently in the past couple of years the clients have me do the products shots on stills, but as well, i have jumped on a few short film projects because i could, because i had a camera pkg. i wouldnt change my purchase for anything.
so in my opinion, which ever camera fits the work you do, the sooner you get it, the sooner it will pay off!