OK... I'm going to pretend I am your trainer with this response so please don't get offended. It's not an attack.
I feel like you should keep Diamond. He's calm and willing and really a great mount to learn the basics on. You know how to climb on a horse and make it go, but you haven't learned alot of the hows and whys, which means you'll never become great at anything (YET). So my thoughts are, you sell ROWDY. And I'll tell you why. He's a gaited horse and you want to do barrels and speed. You need something that is short and compact and built for quick turns and stops. Rowdy is not the horse to do the things YOU want to do. He's a great horse, don't get me wrong, but if you really want to do the speed events, then he's the one that needs to go for now.
My other comment is No to all of the horses you picked. The Walker because he's a gaited horse built for hours on trail but not for the barrels scene. The first QH I love but it's a quiet mount for a pleasure ride, you are looking for an eventer. Now believe it or not, an eventer (speed) does NOT have to be high strung or spirited. I've seen barrel horses that are the quietest in the barn, but they knew and loved their jobs. And they were GOOD at it!
So, this is not an attack. It's me pretending to be a trainer and trying to help you move towards a goal.....
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"