I read that among the various variables in other anatomical or physiological characteristics investigated, correlation with erect penis length is generally fairly weak. There is, apparently, a positive correlation with height which is just barely statistically significant. This means, it is slightly more likely that a taller guy will have a longer erection than a shorter guy.
However, apparently the strongest correlation was a negative correlation with body mass index (BMI). So apparently, all other things being equal, if you want to win the big dick jackpot (or at least the long dick jackpot), go with the tall skinny dude. There may be other factors than the "fat pad" in the pubic region. There could be other things involving fat and metabolism which effect the suspensory ligament system.
Here's a personal anecdotal account. The longest I ever measured my dick was about 9.25", and this occurred when I was about 130 lbs in weight. It seemed to get shorter at maximum boned-ness when I got up to 173 lbs, probably averaging 7.5" during that time. Now I am about halfway in between in weight (152 last I checked), and my body fat index is a bit higher than it was when that max measurement was taken (overall BMI is not as much lower, but primarily because I have much more muscle), and the maximum recent measurement was 8.5".
I have noticed no effects on girth, it has continued to slowly grow in that direction the whole time, for which I hold greater intentional attention to the surrounding muscles responsible, and it may be that girth generally continues to grow through one's 20's much more so than length.
As far as the comments on the tall skinny guys, that was not made either in self-interest or against it -- I am 5'10" 152 lbs. Apparently my BMI puts me in the "optimal" range. It feels so nice to be perfect in some statistic...although I was told before that I had the perfect cock for marriage, whatever that means...
Once again, why is it all about length in these stupid studies when IMO,
it's all about the girth...(there bias properly applies)