You are equating big dick with orgasm, which is really not how sex with women work. It shows you really don't know much about women's satisfaction like you think you do.
A big dick does have its advantages, but it is really not a necessary prerequisite for good sex, and orgasm. The only time it makes much difference is when compared to an unusually small dick.
More often than not, big dick is like a big ass, more of a pleasure to the eyes than the actual action.
Do you want to know why your woman will never forget that guy with the huge dick?
Well, never mind. Your answer is not necessary. I will say it regardless.
The reason women, broadly speaking, do not forget that guy with the huge dick - the nastiest and most ungodly sex - is because orgasm is for women what one's finest hour is for a man: memorable, unforgettable.
As men do not forget their first triumph. The first car, their first big job, or the day they won the lottery, so women do not forget the guy, the sex, the dick that gave them the most intense orgasm, that disvirgined them.
Because those moments, for both men and women, are essentially moments of relief.
And because the need for that level of relief in women is recurrent, she remembers that guy more often than is appropriate.
But I have said enough.
Good luck. Or, congratulations.