Learn English – The right word for an assumption which is very likely true

I can't think of multiple single-word elements that are unambiguously scaled (is "sluggish" faster or slower than "plodding"?) but there are certainly phrases that can be used...

normal -> a bit slow -> slow -> slow as molasses -> slower than molasses in January

(I'd be inclined personally to say that "sluggish" is a good substitute for "a bit slow"--it's slower than normal, but not as slow as just plain "slow"--but I'm not at all sure that it would be widely agreed upon.)

Going in the other direction, you could have:

normal -> brisk -> fast -> faster than a speeding bullet -> at the speed of light

"You will oblige me by taking them" is extremely formal, and much more typical of the Victorian era than the modern one. You might still hear someone in the British royalty say something like this.

Your second sentence is much more common. To oblige someone is to do them a favor, not to put them under obligation to do a favor in return. So no, I don't think that the writer was trying to imply getting something in return. ("Put her under obligation" would very much mean that she owed something in return.)

If you look at old Western movies, you'll see cowboys touch their hats and say "Much obliged." That's a way of saying thank you, that still persists to some degree in places like Texas and Arizona. There isn't any sense that the person saying that is under an obligation (beyond that of human obligation to a neighbor) to return the favor, even though that is the essential meaning of the word.