I see more big cocks on straight porn.
I don't know. A straight friend made this remark before (that gay guys are more hung) but i never took it seriously. I've seen some huge straight guys at the gym. And I've seen small gay guys everywhere.
I don't think there's a practical way of judging from experience because gays tend to have more partners so they're more visible. If a gay guy is hung he'll probably have more opportunities to be seen.
Straight guys will be in steady relationships with jealous girls. And the girls they sleep with can't compare them with gay guys because they don't sleep with them.
I would've liked the hormone theory angle but it doesn't hold well here, I don't quite understand how a lack of testosterone in the womb makes gays produce more testosterone the rest of their lives. If that were true then the gay-er a guy is prenatally, the more masculine he should be from the time adolescent hits. I've seen really feminine looking gays with really tiny dicks. Doesn't make sense.
I'm not saying the suspicion is baseless, I'm saying it might be possible, it's worth looking into. It should be quite easy to run a statistic formula for correlation based on the gender percentages here and penis size. Maybe our profiles should have a field for penis size (length, girth). Might as well include ethnicity. Run the correlation formula on these factors and we'll get closer to the real picture.