Competency wise, D3/D3S is still going to last for another 3-5 years till you get your hands itchy for upgrade.
My D2X followed me through 7 years of abuse in events till now, and it's still a workhorse, and a lovely one still.
D3/D3S was a major breakthrough in FX and Hi-ISO. Compared with the D4, I'd say it's only losing out in MP (not that it's important) and several unnecessary functions / good-to-have-designs.
I've played with the D3S/D4, I'd have considered the D3S over the D4 in terms of pricing as well as the ability to use back the same batteries my D2X uses to cut down on costs. Alas, decided too late, Nikon SG stopped bringing in D3S and I gotten the D4 instead.
Words can't convince you much you need to test it out, but doubt any D3S users will have time to meet up and let you get the 'high' of it. Nikon flagships, hardly go wrong.
A D3/D3S would probably last you a good years until D5 or D6S is released.