What is the ground speed of an unladen Ent?

[Beren87]

I strongly dislike debating the finer points of Tolkien's work

Then don't. But we are. That's more or less the point of this forum.

Anway, I would think an Ent's stride to be around 10 ft?

Oh, not that big.

Let's think about this, I'm abuot 6ft, and I have a long stride of 3 ft. That's a ratio of 2:1. Now, as Prof. Tolkien says, the average Ent was about 14ft tall. If we apply the same ratio to Ents, we get a 7 foot stride.

so didn't have to change their way of walking like we do when we go downstairs without bending our knees.

They were, however, less posable then we are, so staircases would take quite a lot of balance. I suppose maybe there's a slight jump or such involved. A special technique, as it were. But, they would certainly have to change their walk a bit. You have to think, also, that staircases are less of a step for them, as compared to us. While a staircase may be a step 1/7 our body size, they're a step roughly 1/15th a Ent's body size. That's a lot less distance to raise your feet, as compared to the rest of you.