They didn't include the data to see their girth distribution, but if we just go by the lifestyles study (which has that distribution, and has been pointed out in this thread is probably mostly measuring bigger guys since it's a self-selected sample) then the TOP end of the IQR is actually a little below 5.2". The IQR looks to be around 4.4" to 5.1" - so for the non-statslovers here, that's the range where 50% of men's girth falls.
The bottom 5% is below 3 3/4" girth, and the top 5% starts around 5 1/2" girth. Only 1% was above 6" around.
So if you'd slept with an equally random sample of men (the same kind of guys who showed up for the study -- probably the bigger guys), if you'd only slept with 10 men in your life, the odds of them all being 6" thick or more is 1 in 10^20, or 1 in 100,000,000,000,000,000,000, or 1 in 100 quintillion. That's about the same odds as winning the powerball lottery jackpot 5 times in a row.
Even if you lower it down so every guy was over 5.5" around, to have only fucked guys that thick or more (so maybe your average was ~6"..) that's still 1/20 guys that big, so that's 1 in 10,240,000,000,000, or about 1 in 10 trillion.
Not that it's impossible to fuck 10 guys that thick, but the only way for every guy to have been that thick or more is if you specifically are filtering on dick girth.