Well... I am 5'6" with just under 8" for cock length and looks proportionately huge on me. I had a buddy who had an almost identicle cock to me but he was 6'3" It looked normal size on him.
Most porn stars are very short, few are tall for the very reason you state. You got this guy above at 6'7" with a 9" cock..' Huge in every way but it looks proportioned to his body, and on camera he will look 5'10"-6' with a 6" cock instead of reality. A short guy will look like he too is 5'10" with a 7" cock and everyone will think its a 9" cock
Bottom line is, a 9" cock up your ass is huge no matter who its connected to! (get it - bottom line - ;-) )