Change of topic: thanks to (person on this list) who pointed me to
http://********************/studio/333 - just downloaded 7 videos and I have to say I'm impressed, they are everything I was hoping for and more. And no I'm not a shill for the studio. I'm willing to pay something for high-quality fringe material that's probably not in great demand. As you might guess, I found the video clips on Cock Whipping (he remains impressively erect throughout the abuse!), 2 videos with mild and severe cock-biting, and 1 video with a big knife - applied at least 4 or 5 times to her man's very erect penis (it must be a deliberately dull knife because she did some serious sawing with (I think) the sharp edge of the blade, but no blood).
Di's personality is perfect for these videos. She obviously loves playing with the man's cock, keeping him on the edge of coming, and is proud of her technique. She is comfortable and intimate with the camera, looks completely relaxed, and keeps a running hot commentary going throughout the clip. This is good stuff. Thanks for posting the link!