Good morning, I'm including the "makes and models" so you can do your own fact checking if you wish.
Haulmark TST85X20WT2 (steel) OAL - 23'6"; inside L - 20'5"; W - 96"; curb wt. - 3,245; gross - 7,000
Rance RECH818TA2 (all-aluminum) OAL - 24'6"; inside L - 21'4"; W - 96"; curb wt. - 2,550; gross - 7,000
The Rance has a foot more interior length and weighs almost 700 lbs. less, the math says thats over a 21% reduction. 700 lbs. is significant, it could mean a full tank of fresh water, or a third bike in the trailer, or tools, etc. Weight wasn't my only concern, it was a benefit. Corrosion resistance and quality are my two main concerns. In a way it's very similar to the gasMH vs. dieselMH issue, when you buy a diesel you don't just get a gasMH with a diesel engine. Most all-aluminum trailers are simply made better than the steel ones. Heck, Featherlight has a 10 year warranty on theirs, you don't see that from any steel trailer manufacturer. ...and yes, all-aluminum trailers cost more than steel.
trailer 2,550
bike 750
bike 800
2008 Smart 1,650
Total 5,750 lbs. (looks like between 5,500 and 6,000 to me!)
There is a reason Boeing doesn't make planes out of steel!