I'd like to add a couple of things to this discussion from a man's pov.
I would not be upfront about your need, which btw I respect completely. The reason is sinmply that you plant the idea that you are primarily interested, sex wise, in a big cock and that this is a sine qua non for an ongoing reltionship. If I am looking for an ongoing relationship, I don't want it to be reliant upon my cock. Of course I want my cock to be appreciated, but I don't want the confusion as to whether it is me or the cock. I appreciate that it is the whole package, but the stipulation throws doubt on this.
I am far more comfortable if a relationship develops to that point where we want to have sex and the cock is a pleasant surprise. This though is subject to size compatability. I am experienced enough to know that one woman's big is another woman's average, and that in the latter case a woman is getting from 8 what another woman gets from 6. You might find, if you are the latter that a big guy will find you less satisfying than the woman who is happy with 6.
Then there's the girth issue.