Ian,
The buggy I used at the job was a 4x5, when you loaded it full, it held just about as much as you can put in the northtrail. The northtrail is quite a bit bigger, but there is a point where you cant load it full because its too heavy for the ATV, depending on type of wood and terrain.
ahaha yea, i found that out the hard way too up at the cottage. I wanted a softer ride (like the bush buggy provides) on one of our trailers up there, didnt know it was tubeless and 30 meters down the trail with 4 people in it the tire lost the bead and was flat. Thats why i liked the bush buggy, it floats because of the low PSI and cause of the low PSI the tires are just like suspension, it makes it easier to work with, and alot better for people to ride in.