What a read! Haha
I actually came her to post Airthrey Highlander as an example of how far some Draft Crosses can go. It all depends on the individual.
Here in NZ the Clyde TBX is almost a staple, for a level headed horse that can turn it's hand relatively well at almost anything you throw at it. We seem to have perfected the Clyde X TB breedings to a precise art and they are very common in any (english) show that you go to here (obviously not in the park hack ring :P).
When it comes down to it, so long as the horse isn't a trainwreck in body and mind they can do relatively well in the lower levels. Due to the non-existent OP we won't know what level they were aiming at.