5.5 is probably quite big.
Compared to porn stars it might not be, but compared to the average population it is. It’s probably about as common(uncommon) as D cups. 6 inches is probably about as common as DD, and I’d guess for the lucky 6.5+ guys, that’s probably like E cups. 6.5+ is about 1 in 1000 probability. (Meaning it exists, and especially on sites like this, there will be people who measure 6.5+) Remember this is the Internet, where you can find pictures all around the world. It’s probably not too hard to find measurements of 6”+ on the Internet. But in real life, the studies show that only about 1 in 100 people have it. On a site like this (which I assume is comprised mostly of the ‘larger’ segment of the population) I think 5.5+ is probably very common. However, I highly doubt that is the case in reality.
Porn stars are above average just like NBA players are well above average height. I haven’t yet found any study which showed an average above 5 inches. Even sizesurvey.com (which has very different results from other studies) has the average at 5.
There are about 3 billion men in the world. I wouldn’t be surprised if no more than 1 million had 6.5+. And I also wouldn’t be surprised if a few of them were on this site (it turns out some are.)