Are you sure you don't mean Bobbi Starr? (I searched for Brenda Starr, but no porn showed up) I've seen a BangBros scene (Monsters of Cock) with her where she does a pretty convincing job of seeming genuinly excited by Castro's cock. I'm not sure if the actual fucking is as convincing, but the fucking part of MoC scenes are usually shite, aren't they?

As for more 'enthusiasm' from the girls in big dick porn scenes, I'm all with you in wanting to see more of that, but I think, like others here have touched on, the not so sexy truth is that most (all?) girls in porn are there for the money and not for pleasure, and an extra big dick probably just means an extra rough day at work. They seem unexcited because that's exactly what they are.

In addition to those who have been mentioned I think Christie Lee was pretty convincing. I've seen her do Mandingo and Shane, and she didn't exactly seem to mind their excessive sizes..

I've also seen Jewel De'Nyle state her love for big, fat ones on the adultdvdtalk.com forum.. I know that doesn't prove anything, but it seems like a place where the porn people are 'themselves' and not just putting on an act.