The question skews itself by the way it's formed.
There just might be more 4 inchers than (real) 8 inchers in existence, worldwide.
But there's at least two other factors...
The 8 inchers are going to tend to have sex with way more girls, ... so they'll have a statistical over-representation in the sample,
and
There are probably tons of guys 6.5 or so that have convinced some female that it was an 8.
So while there are maybe/probably more people with a 4 than an 8 (imo) , -- the girl will nonetheless be more likely to run into an 8 ... or what the guy has asserted as being an 8.
One thing's for d*mn sure, .... there aren't any 5 inch guys out there going, "Nah Baby ... that's totally a 4!"