The size of my babies has borne no resemblance to the amount of weight I put on - my nearly 10lber was after a pregnancy when I put on the *least* weight

You have a proven pelvis, so that is in your favour. Positioning can help reduce stitches, as, I believe, can allowing the mother to push at her own pace rather than coaching pushing through the crowning phase.

My last delivery, I had no idea she was so big. I laboured upright, and delivered on my hands and knees. I had no tearing or stitches, and it was all very uneventful.