First as you prob know, weight estimates are notoriously inaccurate!
My first baby was 8lb 3 at 38 weeks exactly and I had a 7 hr labour with 2 hrs of pushing on g&a, ended up giving birth sitting up with legs in stirrups (other positions like leaning over head of bed weren't working but in hindsight I think It took me a while to get the hang of pushing!). One small internal stitch. All along baby measured 50th centile on scans.
Second baby (now almost 4 months old) was also average all along on scans and arrived at 40+5 after 1hr 50 mins from waters breaking to babe in arms and ten minutes of pushing. I gave birth to him standing up, had a few tokes of g&a before actually pushing him out.
He was 10lb11. Totally was not expecting that, consultant had the midwives weigh him twice!
I had three stitches for a small 1st degree tear. Have no incontinence issues, though haven't tried sex since birth so can't comment on that - because of exhaustion as opposed to anything else but I am a bit nervous; such a whopper with only few stitches is making me worry my vajayjay may not be it's former self... Gagh.
However I would say big baby doesn't necessarily mean horrific birth or lots of damage. For me #2's birth was much easier and I could feel my body just getting on with it whereas with #1 I never really felt the urge to push people speak of (I had syntocinin at one point as contractions got v short) and it took a long time to get him out. Body really did know the drill second time round and #1 had clearly paved the way so to speak.
Both midwives commented that standing up was probably the best position to give birth in given he was so big, gravity helped. The consultant who delivered him (I was private) however was surprised I was able to stay standing up. When he actually came out I squatted right down to the floor, though this was totally involuntary and I just did it without thinking.
Read Ina May - I read it for both and it massively helped my preparation.
Best of luck!