You're all being too hard on him, I kind of see the point of the post. However, the part about debating whether to buy a camera to only turn around and try to sell it again, seems more a waste of time.
Faxon, if you're interested in buying and selling things for profit, I suggest you try trading stock equities. They are very liquid, and it's very easy to make a profit, but also to lose money. I've mostly lost money, but I stayed in it because I made so much money early on, back in 2004 to be precise. Now I've decided I have to stay out for the foreseeable future, or until I start making more money...enough that I can afford to lose some!
As for your 1D3, I've never used one, but I did rent the 1D4. I liked it a lot. But not enough to buy a used one for over $3k. It could not autofocus in low light. The noise, in my opinion, is not that much worse than the 5D3's noise, but at lower ISO, the 5D3 has a bit more dynamic range. The main difference is the full frame sensor, and being able to go very wide with wider angle lenses...along with a bit more image pixel resolution.
The 5D3's autofocus and ability to shoot RAW video (with the ML hack), are good reasons to buy a 5D3. The 1Dx's autofocus still blows it out of the water.
It really depends on how often you shoot at 8 or 10 frames per second. If you need to do that all the time, just save for a used 1Dx, or else a new one...or else possibly a 7D Mk2 (I've grown very uninterested in this one).
I bought a 6D, and could not be much happier. The autofocus can be weak at times, but it works reliably even in servo mode if you have good light. The AF menu is highly tweakable. I mostly don't shoot in multi-shot mode, but when I do, it works fine. 4.5 fps is very slow compared to 8 or more...but not so slow compared to 6 (as per the 5D3). As for video, I don't shoot much, but have not excited the 6D's moire problem with what I've done.