After using the Mamiya RB and RZ systems, and DSLR's D200, D2x, D3 and now the D3x I am able to produce my most oustanding images so far.
I prefer to keep the ISO below 1100, and generally ISO 100 90% of my shooting time. It also demands my best glass. I have shot many tests using many Prosumer and Pro glass. And the better the glass the better the image quality. Any imperfection in the glass or shooting technique is amplified in the image. My personal choice is the PC-E trilogy of lenses.
The D3x also requires a sturdy tripod and mirror-up to capture the best image.
Since my personal style of shooting has always been tripod based the D3x works extremely well for me.
I also have not had the best images trying to use the D3x as a walk-around body. Probably my technique more than the body. My D3 is still my go to body for general use.
Well worth the high price, if you need the highest quality images.