Not really a big deal on long strips
Can't give you the number you're after, but on a long strip your are likely to be climb limited rather than field limited. The fact that the extra rwy is available to get airborne isn't going to help you if you have an engine failure at V1 and not enough thrust to climb away on the remaining engine.
On a shorter runway, the problem is not getting airborne on two engines but stopping. It will take longer to get to V1 so that by the time you (nearly) get there and you have a failure there might not be enough rwy left to stop.
Since according to your post it didn't actually happen in the end I would call up the performance people and have them run it through the Boeing software they use. Could make an interesting little piece for your company safety newsletter.