Here are some more info on how I work. I must say I am a bit lazy to bring the 70-200. I shoot it on a monopod for sports and sometimes I use it for shooting concerts but otherwise I seldom bring it. My copy does not have OS/VR which makes it a bit more limited for indoor events when the light is not good enough. Maybe I should get the OS version to make it more versatile. But anyway I will get the 85 f1.8 as well as a smaller tele that should be long enough for most other indoor events. It is also much less intimidating as a portrait lens. So I think most of the time I will bring either the 85 or the 70-200 for the long end depending on what I am shooting.
The Sigma 50 f1.4 is a nobrainer since I already have it and it will be even more useful on full frame. So the main question is what to do on the wide end. I do like the thought of the three prime setup but I think to only have the 28 f1.8 there might be a bit limited and not wide enough for all situations, that is why I am thinking to pair it with 24-85 to get more flexibility at a decent price point.
However I also like the suggestion of the 16-35 VR. While I am not a true wide angle shooter I usually find that I use the extreme ends of a zoom most and having more wide angle is always handy. Sitting in the front row shooting a performance this could indeed be very useful. I think faster glass would have been preferable to freeze the action but if the D600 still give good results at ISO6400 it should not be a problem.
Another advantage with the 16-35 is that it would force me to use the primes or the 70-200 for longer focal lengths which is good since it will give me better results than a long range zoom. I think the main drawback for me with the 24-120 is that I would be lazy and use it most of the time while my even better glass would sit in the bag. I think this lens would be a great walk around but since I am mostly shooting events with the Nikon I doubt it is the right option for me.
Then the 24-70 Tamron remains. With the new USM focus system it should also be a serious contender for event shooting and the best compromise between speed and zoom range. The drawback is of course less wideangle than the 16-35 and that it is considerably heavier than the 28 f1.8 solution.
I will see what I decide in the end. I will definitely go to the local Nikon store and feel them out, but I will be happy to receive more thoughts and feedback on these lenses.