Well I would think this is a pretty obvious question, but yeah it hurts more when bigger guys pound. Especially if they are long...it tend to ram the cervix and that can hurt. It really hurts unless I am really turned on. In that case, I love it hurting. Vaginal canals are all different lengths, but can usually accomodate a larger penis when sufficiently turned on. Some women just can't take it. It's just how they are made. If I have been pounded and it hurts (the bad hurt), it feels more like cramps the next day if I feel anything. If a guy is thicker and there are lubrication issues, then that can hurt as well for a day or so. Average guys or smaller guys generally don't have to worry about these things.
It can hurt bad sometimes, but I am very assertive and will speak up. Some women will not. Make sure you read her facial expressions and her body movements. Also, start slower. If you know you have a giant tool that can hurt someone, as much as you may want to, refrain from just going at it. Work her up well and get her turned on. Feel with your fingers first to see if you think she is ready. Even then, don't go full depth right away. You can even ask her..."do you want it deeper?" "harder?"