same principle
Well, not quite, two is less than three....
And, they wouldn't be "in a row". For a start, I would expect Rider's torture of Sakura to be quite prolonged (because it would take her a while to even start
trying to get information as opposed to just hurting her) and, similarly, Caster's torture of Rider would be quite long (because it would take a few days for the evidence to get to Nero). But, there would be plenty of stuff in between.
I guess you do have a point to a certain extent, but a consensual BDSM scene between them would be nice.
Also, what stuff would you have in mind for Rider and Sakura's torture? Or do you want me to suggest stuff?