My .22 Disco with Beeman FTS pellets, which are a tad heavier than 14.3 gr, is averaging right around 840 at the top of the curve and as you know it's the same as your Katana, except of course that your Katana has a choked barrel and the disco doesn't.
14.3 gr pellets averaging 840 fps is nothing to be to upset about from a hunting stand point. Those numbers will definitely get the job done on any small game you point it at :)
Remember,,,,, a DOA nutter doesn't know if the pellet that killed him was traveling 840 fps or 900 fps ..... dead is dead :)
Jeff