Little Sahara at Waynoka OK is 1520 acres, and the website says the dunes are from 25-75 ft. tall. Lots of good trails to ride, and also a place for everyone to drag race.
Glamis is way larger, I have been there 4 different trips of at least a week each time and still haven't ridden it all. I probably spend way too much time on certain favorite areas! The dunes at Glamis are much larger, and there are also huge bowls to ride in. This is by far my favorite place to ride, but also one of the farthest from me.