I've run the numbers, but it's been a few years.  I still lean towards the bunkers.  Less cost/ton and faster loading/unloading than an upright.  By the time you make a good base and buy 10 years worth of bags (and dispose of 10 years worth of bags) I don't think the bunker will cost any more than bags.
I look at a lot of both, and when I see the spillage around the mouth of the bag, I think shrink can be managed better with a bunker, if sized right, inoculated, packed properly, covered, and the face is managed properly.