Today I went to use another 24 70 ii, and the first copy I looked at must have been a dud. This was much better, I know that you can correct vignetting post processing, but its really not a look which I like in my photos (personal preference).
I think I will rent a copy of a 24mm just to see how it is with people photography, but i can understand how it can be too wide.
Thanks for your help guys