I've heard very good things about AKs chambered in 5.45.
In the late 70s when Russia invaded Afghanistan, they brought along their new AK-74 rifles and carbines, and needless to say, the Mujahideen militia fighters (usually armed with SKS and AK-47 variants) were quite surprised by the round's effectiveness. It absolutely destroys soft tissue and punches right through most light to medium armor.
If I were to purchase a rifle in this round, I'd probably purchase an AK-74 variant with old polymer or wood furniture, not only for shootability, but for the historical value and the ultimate 2nd kind of cool.