As for top 5 backs
SJax is a pipe dream. That team is DONE. He's not going to have a year, LET ALONE be a top 5 back from here on out... he's not playing this week... so "from here on out" he's still at least one game behind anyone else you can name. So if he's not back next week (which I don't think many people expect) then he's got the bye week... so "from here on out" there's a running back you'd like who has a MAXIMUM of 6 games, vs several great starters (such as FWP) that have better teams, better schedules, and NINE to score in? That don't make no darn sense, brother.
It would be different if we were talking about a guy known for putting up freakish numbers, like an LT, with a team around him. But if this guy comes back, he comes back to a cast of walking dead, with no real hope for the season. Steven Jackson is the guy you wish you traded right before the injury. He's dead weight on your rosters now, and when he comes back, he's a RB2 because of his team.