The 6 player doesn't have a database tab. Not sure what that means but it's not there. Was it there in the K5 Player (I've always had the full version so I'm not sure).
I installed it, ran a few tests. Doesn't seem better/different than my full V5 at anything. CPU looked the same, nothing was faster or smoother or better.
In fact you might have a hard time even telling you were using 6 instead of 5. The differences are that minor.
But 6 doesn't replace 5. It won't upgrade your old projects (player or full) it's a whole new plugin/etc. So you'll have to keep 5 installed/etc.
I think given Kontakt 6 was the main reason to buy the upgrade to Komplete 12 for me, based on what I see here I'll wait. In 9 months they will have the summer sale and the upgrade will be half priced. Until then any K6 required libraries I can use in the K6 Player.