If you have a x39 that shoots about MOA and taking short shots you don't need a different gun. But if you need an excuse then absolutely the 6.5 Grendel is a better mouse trap. I don't know about the CZ as I've never had one, but have seen some great shooting AR's in Grendel. To be honest though, at the short ranges almost anything will work with the right ammo.

“You never need fear a man, no matter what his size. When danger threatens, call on me, and I will equalize.”
Samuel Colt.

�Common sense is genius dressed up in work clothes.� - Ralph Waldo Emerson