There has not been any change to the production capacity of a farm plot in 0.40 so far.
But as I said previously, dwarf consumption *has* changed. A quick test reveals that idle dwarves are approximately 10% thirstier in v0.40 as compared to v0.34.
The wiki, by the way, claims a fully-utilized 3x3 plot *is* sufficient to supply a mature fortress in v0.34.
Whoever wrote that didn't show their work. I assume they mean some combination of quarry bushes for food and plump helmets for booze, and magically preventing the dwarves from ever eating a raw plump helmet, and using fertilizer, and having enough Legendary+N planters that at least one is on duty (not on break) all the time, and probably some other voodoo.
The numbers are cleverly hidden in that big table in the middle of the page. Using straight plump helmets:
Average stack size(5) x harvests per year (12) x brewing multiplier (5) = 300 alcohol per tile per year
300 x farm tiles (9) = 2700 alcohol per year.
2700 / ( drinks per year (16) + meals per year (8 ) ) = 112.5 dwarves
Possibly this was calculated back when straight booze-cooking worked, but adding a few plump helmet spawn to the ingredient list should have your kitchen making bountiful wine roasts just like old times.
It does require the planters to be on task, but an average stack size of 5 appears reasonable, especially with fertilization.