I feel like OTQHs are great candidates for barrel racing.
I know that you, personally, don't rush anything in training, and that's (I believe) the only reason that a lot of the QHs I saw off the track and running blow up. I actually met someone at a show who got his right off the track a month prior and had him running the pattern and bragging about it to Drew and myself at the show about how quickly the gelding came around. All I could do was stare at him with a fake (yet believable, apparently) smile and nod my head to him when he started going on about how he just got the horse off the track last month and how quickly he trained him. How he won a ribbon with that horse..Horse wouldn't stand still, wouldn't stop (even with the big ass shank he had in his mouth), didn't want to turn at all, etc. I felt absolutely horrible for that horse, but hey..none of my business. :\
Anyway..moral of that^ ramble. If someone would have taken the time to let the gelding come down and put a solid foundation on him, he would've made an absolutely amazing barrel horse. With the spins and turns he was making (not on cue, mind you..) and the speed the horse had between barrels, he would've had any of the classes I've been to, hands down.
I'm actually hoping to get a few OTTBs and OTQHs when I get a chance. I'd love to have a full 2 months of just taking pasture pictures and some groundwork. Even though I love training and showing, just seeing them learning how to be horses appeals to me greatly. That way I can blow my camera up with pictures and spam you all.
But..main point, as long as they're not ran into the ground and allowed to be crazy (like some I know..*le sigh*), I think they'd be perfect for barrels, just need to know how to pick 'em. Obviously not all of them will be suited for barrels, but since I plan to do all sorts of western events (aside from pleasure), I'm sure I'll be able to do something with anything I got off the track, even if it's just a pack horse for camping. :p