Performance involves a trade-off. The <i>optimum performance setting</i> will depend on how much <b>you</b> are willing to trade.
Best performance will be with QLIBLCKLVL set to ’0′. That trades a performance boost for some drop in security (as in anxiety level, mostly; but also some protection).
I’m not sure anyone can help you with “optimum”. Without detailed knowledge of your system environment, no one knows. A setting of ’0′ performs better than a setting of ’1′. That’s about the limit of what an outsider can say.