This is great. One thing I like is that neither of them are Mary Sues, I'm not sure whether I even like them that much, you've extrapolated what they'd be like really well, I think the 51st Century characters we know, Jack, River and John Hart all have similar traits.

I really loved Ianto's first glimpse of Jack, excellent bit of exposition, so Ianto has known about Jack for a really long time.