no offense, but if he can full out gallop and race... what ARE his so-called limits? Galloping is kind of the hardest thing a horse can really do, especially on his knees (hence why so many OTTB have bad knees).
A lot of people think their horses can do much more then they really can, simply because they don't look at the situation in a realistic manner. A weak-kneed horse is simply NOT a candidate for racing, or even a little one with a rider on his back. I'm sure he could get away with it, but that doesn't mean he's comfortable (just because he loves running doesn't mean it doesn't hurt). Also, it's how horse's break legs on the track--they have a little 'wobble' because of their knee, take a bad step, and BAM! Broken leg. And guess what happens to you when your horse slams into the dirt at 35 miles and hour? Trust me, it isn't pretty.