Similarly to Annie, I was taken down to theatre for a c-section after 32hours of labour because the midwives (and doctors and anyone else who fancied a look up there) were concerned about the size of the baby, and because of her enormous bonce she had gotten slightly stuck. After she was born (naturally, she popped out the right hole by herself in the end LOL) they said they thought she was going to be at least 10lb but she was "only" 8lb 9oz.
I honestly, don't think that the size of the baby has anything to do with the length / intensity of pain. Let's face it, unless you have a baby smaller than an apple it's going to hurt considerably.
I think everyone knows someone who has had frighteningly quick labours, equally frighteningly long labours, early babies, monstrously late babies, huge whopping dumpling babies and tiddly little dolly babies - ultimately, the end result is the same, within minutes you will be gazing in wonderment at your little bundle muttering "I don't know what everyone moans about....".
Good luck lsharp, I am sure everything will be fine xx