Interesting post, Mattbrick. I've never been a sperm donor, but I also have unusually large testicles (see my gallery), and with me that's also correlated with an extraordinarily high sperm count, which I had checked when I was 20. In my case I ejaculated about 7mils for the test, I had around 137 million per mil, which gives a total count of about 960 million. So yeah for me- big balls = lots of sperm and semen.