Mia apparently comes from CMK (Crabbet, Maynesboro, and Kellogg) lines. I don't know much about breeding, but I gather they emphasized endurance and military sales (back when the military used horses). Her sire tended to produce horses pushing or hitting 16 hands. Mia's estimated weight at her last vet check was 890 lbs.
Lilly is more what people think of as Arabian. She was 14.2 and weighed around 750. She carried me & my saddle pretty well, but 200/750 = 27% and she took a while under saddle to find her balance with me. Once she did, she didn't seem to have any trouble. Small, light, lots of spunk combined with a gentle nature...great horse. I would have kept her, but the rest of the family voted to keep Trooper, who in all honesty is probably a better horse for general riding.
A picture of both below, with me riding Mia in an English jump saddle and my youngest riding Lilly in a western saddle:
Both are good horses, and Lilly's new owner is riding her on trails3-4 times/week.
Oh, and while Trooper is an Appaloosa, 3 of his 4 grandparents were pure Arabian. It is a great breed!