FWIW I'm pushing the 4400lbs alko axles on one trailer. so I talked to my local parts guy about just what the 4400lb axles are. After he talked to Alko, best he could tell, and what he though earlier is that the 4400lb axles use a 5200lb tube, 10" brakes instead of 12" like the 5200lbs, usually 6 lug wheels and a spindle/bearing different from the 3500lb or the 5200/6000lb axles, and 2200lb springs.
As long as you have 4400lbs with 6 lug wheels rated for 2800+lbs you can switch to 5200lb axles using the same wheels and get more margin and bigger brakes. 225/75 LRE tires have a 2800lb rating so they have some margin.
curious if anyone else has info on what the 4400lb axles are composed of.
With almost 4400lbs on mine with the WD hooked up, the tubes still have lots of camber in them, and after 20K miles tires are wearing evenly. so I guess the axles have reasonable margin.