Also, I've still got a spreadsheet worked up to figure the profit of different goods and if you should take a wagon or elephant. Very few goods are actually worth taking a wagon on, the vast majority store more in an elephant.
Did you account for movement speed though?
There's a difference in movement speed, but it's not fantastic, and for most items you want the biggest single-load value AND that turns out to be better than "gold per minute" rating.
To really get a handle on the "gold per minute" figure, you'd actually have to figure out how long it takes to reach each location from each other location, and variables to routes (some are faster, but more dangerous and not used) and natural sway to how you click the map compared to others or if you spend time idling briefly.
Even if we don't know the speed, I have the numbers for profit on the last time I was calculating, however many months ago.
Topaz was +163 per unit in profit. A wagon can carry 36 and an elephant can carry 68. The profits for each were ~68k and ~128k. I really doubt the cart moves at 180% speed.
For the most part, items are clearly better on wagon or on elephant - namely, low-tier items (coal) go on wagons, but high-tier items (topaz, ore, etc.) go on elephant. The nearest questionable items are Ginseng from Tir, Music Boxes from Taillteann, animal products from Emain, and oysters from Cobh. All of these fit 300 to the wagon and 350 to the elephant, which is 116% - the cart MAY go faster than this, but this is really the closest margin. The rest are at LEAST 140% with most in the 168-180% range of difference. (For items that are better on the elephant, at least. I didn't count items that are better on the wagon because that'd be pointless!)