I'm wondering why you're wanting to replace the XO-3, which is quite a nice bike. Unless you are in love with the convenience of brake-mounted shifters, perhaps the XO-3 just needs some maintenance. Given that there are no mountains where you live, reducing bike weight is not going to give you any advantages unless you are wanting to win sprints, and a carbon bike will be more fragile than anything made of metal. IMHO weight is irrelevant to non-racers; your only real concerns should be fit and overall quality/durability of components.

Full disclosure: I got rid of my modern bikes some time ago and now solely ride vintage steeds (and frequently beat my friends on their carbon bikes, even when riding our west coast mountains). I guess you cold call me a retrogrouch.