It seems like submissions being reviewed in PR # order could encourage edit camping where you can continuously update a PR with new results and keep your old position in the PR # review queue.
If @0hq @valerio-oai want to keep reviewing submissions in PR # order then I think it would be reasonable to impose a maximum bpb change within which you can edit an original PR's results. If changes are greater than a certain bpb threshold i.e. 0.002 you would have to open up a new PR and get a new spot in the review queue.