I have a 7000lb [AFFILIATE=1, nofollow=true, newwindow=true, title="Kubota"]Kubota[/AFFILIATE] KX91 and have built a few walls with some rocks over 1500, around 4' -5' high. My machine is not a zero-tail machine so I do have to watch the hangover but it was able to build the walls without any drama. You learn to work with the machine limits - get closer, use your blade to lift the front of the machine to get a bit higher when needed, and things like that.
the attached photo shows one rock I dug out and then moved across the property to be used in a wall. To carry it I set the edge on the blade to take some weight off the boom and tram it around a bit easier. I don't know the weight but it was HEAVY.
Also, are you towing it all the time or just to get it home? If not, have it delivered from the dealer when you buy it, and you avoid all the trailer issues perhaps.