I never did get a pair of boots at the Royal...didn't ever find a pair in the right size.
For those who have tried different brands/styles, it appears to me that based on the hoof conformation of my lease horse...not every style will actually fit. I have to get a new measurement this weekend as I'm not 100% confident in my original measurement, but it appears that (based on what I have) that some style boots will fit, but others are simply unsuitable - one size is good in the width but not in the length, and the next size either side is the opposite.
Option B is speaking to his owner about getting him shod instead - I'd be willing to pay the cost, and he's used pretty lightly so I'm sure they would prove durable. My only concern there is that he likely has very typical thin walled TB hooves that I've heard/read can be problematic to shoe. Again, I'll talk to his owner, I'm sure she'll have some insight.