Upload & Sell: On
Your description of how you think your chances would improve if you had 12 frames per second is not real clear. The theory is that if you go from 6 fps to 12 fps, your chances would double. So your self described 5% keeper rate would go to 10%. A 1D4 at about 10 fps would be in between. If that gain to 10% is worth the extra $5,000 to $7,500 in cost to get or upgrade to a 1DX, go for it.
The 1DX is a very very nice camera, and I am glad I got mine when I did. I rarely use all of the 12 fps, but I really like the excellent autofocus, the low light performance, the very accurate auto exposure, the full frame, and all the little things like the built in camera level. But I do not like hauling around a big pro body on hikes or holding it for long periods of shooting, which is why I also just upgraded my 5D2 to a 5D3. A 1DX plus a 5D3 is a nice pair, but do not ignore the used 1D4 option, which is a very nice camera for action, and has that extra reach.