I just came across this forum online. My wife prefers white guys. We are active in the lifestyle and she's had many men over the years.
One black, no Asian, dozens and dozens of white guys.
I think it's a bit of a myth that bbc are the biggest. I think it varies irrespective of colour. I have seen some absolutely massive cocks in her, and they've all been white. Yes the black one was big but it wasn't in the top 20 or 30 of what I've seen.
Back to the question though, she said she just prefers them, she's more attracted to them. Weet when I lived in Asia but now we're in the west. Even over there though she'd only agree to fuck other guys if they were white. It made it more difficult to find, much easier now.