I haven't ever touched a D3s. According to Ian Hylands, the D4 image is 'different' than the D3s, but was reluctant to comment which was better. Obviously slightly more resolution in the D4. Ian says the D4 files 'do not require sharpening in post'. The handling as you mentioned is great on the pro bodies, which is the main reason I opted for the D4 over D800. D700 is such a great camera. I will probably never sell mine. D800 would be fine for action, so long as you don't need the high frame rate. Autofocus on the D4 is superb, even at the full 10fps, and they say D800 has the same AF. Only problem with the huge files is hard drive space, which is why I initially did not want a D800. Plus the fact that I needed a video-capable camera now and D4 was available months sooner. Thanks for the props!

 High ISO quality is phenomenal, which helps a lot in the dark woods around here. It's big and heavy, which is good for shooting but bad for carrying. Battery life isn't spectacular. Video is soft, not quite what I was expecting. Super sharp RAW photo image files. Better weather sealing than any other Nikon. It's nice, but beyond necessary for what I do. Considering the D800 instead, just not stoked on the huge RAW file sizes.