Really, this depends how you work. If you don't shoot in extremely low light (ISO3200, 1/60th, f2.
the 5dii's centre point should be accurate enough for your needs.
If you want to shoot with other focus points than the centre one, you really need the 5d3.
I wouldn't buy the 5d3 based on the high ISO improvements if I was you. It's about 2/3rd stop in RAW and if you don't shoot over ISO1600, it won't be that noticeable. P.S I shoot in RAW and processes in lightroom. That in itself has got me fantastic returns in terms of high ISO performance.