OK - in a gig environment, I reckon the real world difference would be minimal, especially when considering the average punters ears.. and especially if the things are being deployed with subs. But I concur, the 745s seem to go a bit deeper but at the expense of tightness (this would be a null point with subs I suspect). The top end is a bit more fizzy. The midrange is a little thinner on the 745, compared to the warmer, thicker midrange in the NX. I think the NX is a better sounding cab - although those that are used to a more hyped top end and a hankering for cut mids, I suspect will prefer the 745s.
Yes, I like the NX - but probably not enough to actually change. Mind you, I'd have to listen to them in person before making such a decision... but given the fact that I haven't left the house in 4 months, I don't think I'll be using any PA equipment any time soon.