Out of curiosity: is anyone aware of any top rodeo horses (or futurity, etc.) that have been confirmed to have any PSSM variant?  

I’ve had several PSSM 1 horses in training that have been easily managed with diet. All of them have went in to be successful. Some are rodeo horses and some only jackpot. I had one a few years ago that went to the circuit finals and is a top 1D horse.

Ive had some others that I suspect were P2 that took more to manage but did fine. Had one with RER that has done well.

I've read that Lindsay Sears' Martha has PSSM, but I'm not sure which type. Here's a Western Horseman article that mentions it:

Sugar Moon Express (Martha)

I have worked with a number of PSSM horses that had successful barrel careers. Some you would recognize. If managed properly, they can get along well. A lot of people have heard me say “ they aren’t for everyone “. This is so true. But, If you have the time to keep them active daily, and feed a proper diet, they can have a performance life according to their basic talent. 

MUCH of it depends on what variant(s) are involved.  People who say blanket responses have obviously not really dealt with the different variants.  PSSM1's management is a LOT different from other variants.  Which are you referring to?