You won't. This is not a measurable statistic. Nobody can generically be a "top 5% programmer."
There are top 5% people in video programming, audio programming, cryptography, web development, embedded systems, etc...
And even then, unless you have a way to see the salary and work history of every single one, you cannot make a fair comparison.
Assuming you could see that info, you could get a rough estimate but even still, maybe one place considers someone to be great when another place would consider that same person to be mediocre and not even pay them as well.
Work is highly subjective and each company has his/her needs. Just because 1 person may be a super skilled web developer, doesn't make them a top 5% programmer at an organization necessarily... Maybe the technical challenges at that org are not that profound and the organization lacks communication between teams.. At this org, it would be more beneficial to hire a less-skilled technical developer and a person with better communication skills.