first off welcome to the site
next, as for what is HIGH hours on a skid steer, I think when you get up past the 4000 hour mark, your in HIGH hours, IMO
but keep in mind, that hours alone do NOT tell the story on condition or possible failures, of a macine,
there is a lot more to consider,
HOW the machine was cared for or NOT cared for matters, same as how the machine was used, or abused
a bad owner, operator can ruin a machine in a short period of time, where as a well cared for machine can last a LOT longer than normal!
there are tons of web sites that show spec;'s on machine models, I'd suggest looking at one of them to compare the specs of the machines you listed, to find out differences,
as for other machines to consider,
look at them two machines your considering's spec's and match them up with other machines that have similar features, weight of machine, HP< FLow rates, break force, and so on!
I would personally think if your using a machine for breaking concrete up, you want a HIGHER HP and heavier machine, to take the abuse of doing that work!
I would also, be maybe considering a CTL (compact track loader), from my point of view , they seem to have more stability when loading slabs that extend past a bucket or with a grapple, and many can be had in heavier weights to again handle the abuse a breakers adds to things!
I ideally I think you would want an excavator for the breaker work, if your going to be doing a ton of concrete work, just seems a better tool for the job!
also, keep in mind having good dealer support is valuable, so try and stick to brands that have dealers near you!
as down time can be a costly things, off brands can me longer waiting time on parts, shipping and ordering online is great, but these days shipping can be a gamble and a lot of down time
so having a good dealer with a good parts supply on hand is worth a few extra bucks when buying a machine IMO