I have almost no personal experience with Checkmate foals–I only know one personally who was born this year to a friend, so no idea about his temperament or mature height. That being said, I really like the stallion and have already purchased a breeding to him to use next spring. Jennifer is great to work with.
I have two Bliss MF 3yos who are just lovely–he definitely improved the brain on both, but I would say he doesn’t add height, and maybe detracts from it.
I love Apiro for hunter babies–all the ones I’ve met have had very ammie-friendly temperaments and are big and quiet. I have one due this spring, though the dam is very quiet as well. But he’s got a ton of offspring doing well in the hunters at all levels, so he’s proven to add bone/height/brain. He stands at Avalon, and Kathy is fantastic to work with.
The Argentinus lines and R-line Hanoverians are all well known for passing on great temperaments, so that might be a good place to start. If you have a WB registry in mind, look at what stallions are approved with them, and then google their offspring, etc. Luckily, with a Cabardino mare, you already have that amazing jump, so you can mostly focus on something with the temperament and height you’re looking for.