"If you store them upright, the vinyl pages will curl over time not matter what you do to prevent it."

There's actually a very easy solution for this... if you overstuff the binders with pages (so there is no more room on the half-ring) and stand your binders upright (so there is no room between binders), the pages will have nowhere to go to collapse or bend. I have lots of binders stored vertically and none of the pages curl.

I'll agree, though, that if you do not overstuff the binders and leave ANY room for the pages to move once the binder is closed, the pages WILL curl.