I think "#1 overall pick" is usually not a good way to evaluate... Because if you have the #1 pick, your team sucks in MANY ways.
And if your team sucks that badly, you might have numerous ownership/management/coaching issues that can't be solved by a QB. Good organizations rarely have the #1 overall pick.
That said, I wonder what percentage of Super Bowl winning QBs won it for the team that drafted them? And what percentage of THOSE were first rounders?
It's all about roster construction, and I wonder if optimal is that you get your QB through the draft or whether it doesn't matter if you get your QB from the draft or trade/free agency and use your draft slots on other positions of need...