I'm biased since I have the ivorie GM Bowling and I've been using it pretty much every day for my work bag. Since you have a couple of white ones, maybe you just tend to gravitate towards the classic color more so than the cassis? Do you think you would grab the cassis w/o a thought when you go out or would you end up grabbing one of the white/ivory bags to go with your outfits? Do you have bags in other colors? If so, do you wear them often? Which color bag do you reach for the most when you go out? That may help you decide.
Good luck making that decision and let us know what you end up getting!