At bottom the haters miss the point. Canon gave them the 1DSmk4 without the weight and at half the price.
As the 1DS3 is used mostly in portrait in studio then the gripped 5D3 is actually heavier
The 1DS3 still has less noise in the 50-200 iso range than the 5D3
The 5D3 has the latest advances in technology and I have little doubt that is a great update to the 5D2- but the focus still has to be - does it produce a better image than the 1DS3?
Used 1DS3s are cheaper now than a new 5D3 so the decision is harder. The real test will come IMO in comparing the 1DX with the 1DS3 - the 'official' replacement. Will the low iso noise be improved, will the low iso DR be increased, will the 18mps 1DX stand up against the 21mps of the 1DS3
An even more interesting comparison for the people who demand the lastest technology will be comparing the 1DX to the 5D3
The 5D3 and the 1DS3 cover different market segments and both are fine cameras but the 5D3 as a replacement 1DS3? Close but no cigar