I had a mustang mare-she lived to be about 30-I rode her English & Western-I bought her pregnant, then later she had a foal by my stallion, she would do everything, go anywhere & looked totally different under saddle than just standing in her corral. She was a fun horse.
My problem is I'm a big-frame woman (5'5", 200 lbs) and I think I'd look weird sitting on one. Plus, most of the mustangs I've come across were just under 15hh. Not exactly the right size for me.
Actually, you might be surprised. Both my mustangs are very thick and stocky and are perfectly capable of easily carrying folks a lot bigger than you. I don't know about other mustangs, but my 2 have big barrels and they are just all-around hunky. I'm also 5'5 and my gray boy fits me well.
Koda, the one that I sold last year, now belongs to a woman much bigger than you both in height and weight and I think they look good together.
Also, Koda is only 14.2 but probably weighed close to 1200 pounds.
Eolith made another good point. There was a member here that had a mustang that looked almost identical to my Dobe, only theirs was almost 17 hands tall. I think there is a particular herd in, perhaps, Oregon that is commonly taller than other herds because they have draft blood closer back in their lines.
Just an FYI... I adopted a 2 year old from Warm Springs HMA in Oregon on an online auction. He was listed as being 14.2 hands. When we picked him up at a satelite adoption here in the east he was actually only 13.3 hands. Still an awesome horse, and I'm hoping he'll make 14.2 hands when he's grown. I'm just saying that those yearlings they have listed as being that big may or may not be.