If you're really interested in a Mustang, you might also consider waiting another month. In November they're rounding up 1,000 horses from Wyoming, and there will be a ton of them in Rock Springs to pick from. Wyoming's known for having Mustangs with a lot of draft in them.
I almost went internet adoption, but I'm thankful that I didn't. There's a lot more to choose from if you go to an in-person adoption and you get a better feel for their personality. It's still not perfect, of course, because they change a lot when they settle down, but it does help with the whole gut connection thing.
Pryors are gorgeous! But... they're also overrated. Maybe I'm bitter because I got soo sick of the non-stop drama over their round-up this year. No one cares about 1,000 horses, but 60? That's serious! At least you know none of them would be at risk of going to slaughter - they're too famous. :p *rant over*