.. at the risk of offending some of the purists ...
(1) aerodynamicists and piklots mean two different things when they talk about yaw .. I wouldn't sweat it too much, though. Probably "slip" or "skid" is more meaningfully appropriate for the pilot community
(2) however you arrange it, you need to get more grunt (throttle), less drag (nil slip/skid), and less power required for a given climb/descent rate (suitable speed). So far as balance is concerned (which is the thrust of your question, I suspect), the aeroplane needs to be manipulated so that there is no slip/skid and the flight path appears to be steady to the pilot with constant body angle and airspeed. The climb performance will deteriorate in a turn due to the increased load factor (similar to a level climb at higher gross weight)
(3) re (1), the aircraft is yawing from the pilot's perspective but there is no aerodynamic yaw of any significance if the flight path is constrained to have no significant slip/skid
(4) not so simple as just a matter of looking at one parameter. Certainly no slip/skid will improve performance.
(5) suggest that you have a look at the websites in the tech log sticky and also run some searches on OEI operations in tech log and flight test forums.
Looking at the original intent of this thread, it is important that pilots understand that the ball is reacting to the net force and really doesn't know a great deal about what the aircraft is doing. .. works pretty well in normal flight but needs to be interpreted with care OEI as it can, and will, tell fibs if you give it a chance .. hence the proliferation of slip or yaw strings in aircraft where performance needs to be optimised.