please consider this patch. It adds a new scrolling mode, where you get to the next page in a fixed number of spacebar hits, which does not depend on screen size or page size. View positions are uniformely distributed through the page. More exactly, scroll distance is calculated as (page size - window size) / (hits_number - 1).
I find this mode very predictable: you always know which part of the page you will see after you hit spacebar. On the other hand, with other modes the last scroll on some pages can be as small as 1px, which is rather irritating.