What is the other half? I currently ride a Trakehner/Arab cross in lessons and she's really nice; just under 17hh, really smooth, big gaits and pretty level headed.
The other thing you have to think about is that, unless you breed back to an Arab, you most likely won't be able to register the foal. While you can't ride papers, if you ever had to sell said foal for whatever reason, that is one thing that everyone looks for. Most people will probably tell you to buy a horse/foal that is already on the ground with the traits you are looking for because it is unclear what you might get. You could get a horse that is the same height as her with the bone density of a warmblood. It's tough to know.