I'd say if you were charting and doing your opks and stuff that your O date is more on and to stick with that date. Did they change your due date based on the baby measuring big?
Both of my DSs measured big as well. My son's were 8lb5oz and 8lb8oz, even though I gained 60+lbs with DS1 and only 35-38lbs with DS2. My midwife seemed to think (with me anyways) that with both my boys being the similar in weight that it could be that that's what my body has determined to be a "good weight" or something like that for my kids. So we'll see! I am expecting another "big one" this time too.