Many moons ago - well approximately 4 years give or take, i asked my wife to let me have a budget to by a 5D2 to replace my 30D or 40D. When she was given the price of £2100 the smelling salts were in great use.
That said, budget was given and i purchased said camera and on taking it out for its first shoot, she was impressed in the difference in almost all aspects of the pictures.
ISO800 was not something to be used in emergency - ISO 6400 became the extent of the usable range. The level of detail captured and ability to crop were also something she picked up on quickly. Over the next few months, as the number of 'keepers' increased - she grudgingly accepted the investment was worth while in so far has what "equipment could do to help me improve my photography".
Unlike you, i had already invested in L class lens so did not have that aspect of choice you do. My one and only gripe with the 5D2 ever, was its 9 point AF. Like you, I'm not a center point AF person - i like to choose the AF point according to shot, and sadly all i can say is - i learned to work with the 5D2 AF system.
5D3 AF is a whole new ball game - i don't own one but have tried it and it would be fair to say my gripe has been remedied - and i think you would be happy with it as well. So in that respect, the 5D3 would be a valuable investment to your photography. We've already said how good ISO is on thr 5D2, and it is no worse on a 5D3, so that's most bases covered.
As for lens option - i really would suggest renting the 50 1.2, 85 1.2 or 135 f2 and seeing which floats your photographic boat the most. I've used the 85 1.2 but didn't get on with it - but i think i was the problem, not the lens.