Based on advice (for lesser mortals) in another thread (http://www.canonrumors.com/forum/index.php?topic=23719.0), I would make a completely unqualified recommendation for another 1Dx.
Having two the same makes everything simple, either will do, neither is a favourite.
I'm not in a situation to do this with photography, but I apply it every else that's practical - computers, travel gear, clothes.
In support of this I agree that you will not see a 1Dx II, until the latter half of next year even if it is launched in March. Secondly, there will surely be a decent market for a used Mk I, when you sell both!
Buying for business, it's just a tool that either earns an appropriate return or not. As an individual, emotion and irrationality tend to creep in to the purchase and sale decision, making a rational decision more difficult.
Just my opinion, sometimes I listen to my own advice, and sometimes I don't!