Ian - the 24-85 is an outstanding lens in every aspect especially in its contrast and lack of excessive distortion at the wide end (compare that to the competitors) and color reproduction. If this and wide angle is important to you, then you know the 28-80 will not cut it and then there is only one choice. If you don't have the cash, then there is also only one choice. BTW, grey market the 24-85 is about $800 which is quite cheap compared to say Canon 24-70 L and Nikon 28-70 AFS (all are way over $1k and much heavier and bulkier, if you believe it).
Good luck with your choice