Thanks Guys for all of your thoughts... I might have to reconsider my options.
I very much like the 1D MkIV but the reason I was thinking of changing was purely for noise. The 5D MkII is way better then the 1D4 in that respect, so changing to the 1DX was my first thought. However, it is more sensible as suggested to have two bodies, so may consider the 5D MkIII, and sell the 5D MkII. Only problem I see with that is the resale on the MkII's now is very low, since you can buy a new one for around the $15/1600 dollar mark.... so how much will I get for my MkII + Grip ? Are the batteries on the MkIII different to the MkII ?
Thanks for your input, very much appreciated...