560/1 is arguably one of the most awesome production knives ever made.
The XM takes it up a few notches. The biggest things to me that were improvements were:
-blade grind (spanto) and geometric design
-easier opening with thumb studs
-smoother operation and smoother lock (goes along with the above)
-greater lateral stability (goes along with the above 2)
-S35VN blade steel with excellent heat treatment
-more refined G10 (and dual color ones are awesome)
-very robust hardware
-improved contouring
-better spine serrations (and lock bar serrations)
-heavy emphasis on stonewashed finishes (which hold up really well to usage much more so than many coated/high-polish blades)
-MUCH better carry profile and comfort in carrying (to me this is the biggest improvement)
-and the ability to get service from a smaller company in which I think interaction is a little more direct (Rob has replied to every email I have ever sent them within 24 hours with straight-forward information, which makes my interaction with Hinderer easier as it requires less effort to get things done I need)
(not that the 560 is lacking in any of the above...the XM just further improves upon them)
It sounds like you need a knife that is designed for harder usage...in which case the XM is a great choice as it's really built for the purpose of seeing heavy, and almost abusive, usage. Yes, it's quality and refinement is exceptional, but at the end of the day it is a knife built to handle the worst of the worst.
I think most owners of the 560/1 who go to a XM quickly appreciate the improvements but also appreciate the ZT even more. I started liking my 0550 and 0560 actually more after getting a XM as I really appreciated the design steps KAI took which for a production knife is very extensive. Even on the Thermite, Kershaw did a fantastic job in making a knife that can perform very well for its respective class at a value that is excellent. I think KAI's design considerations is why RH chose them to work with.
For a knife that one wants to be capable of hard (almost abusive work) but without sacrificing all ability to perform certain light tasks in which precision is desired, the Spanto is a great design. It favors harder work, but it can perform virtually any task. It without doubt gives one of the strongest tips on a useful blade grind. I also find the Hinderer to be designed with the flipper as a secondary opening mechanism and the thumb studs being the primary, which I personally like. But I think the way they add traction to the flipper makes it easier to use than most. The only downside to me is the price and high premiums the knife gets because demand is much greater than supply. I've red some people who do not like the usage of the plastic/teflon washers, but I personally really like them. When used with something like Extreme Fluoro grease, the knife is as smooth as any knife I have handled and it keeps that smoothness for a long time between cleanings.
I have read that the XM 3 and XM 3.5 inchers are completely different animals. I only had a 3.5 at that point, but later had a chance to handle the 3 and must say I really agree. I personally find the 3 inch more at home with no flipper and a slicer grind, and the 3.5 with a flipper and spanto. That's just my personal take, but that illustrates that the differences between the two are pretty pronounced, and much more so than say a Mini/Full sized Grip, or Seb 21 large/small.
So I think you will absolutely love the XM, and will also like the 560/561 even more!
