In general you get better efficiency out of it if you set the low-temp down to 140F (for oil burners), or 130F (for gas or propane), with the biggest possible differential hysteresis. Very few hydronic heating systems actually need a 200F boiler temp EVER, so dial that back to ~180F first, see if that fixes the temperature overshoot. If the aquastat is mis-sensing the temp or has a delay and the thing is overshooting, you may need to re-set the element in the sensor well. If the pressure is going off the charts you may need to re-charge or replace the expansion tank on the system.
Whether turning down the water temp will work for you from a heating-the-house point of view depends a bit on how much heat emitter/radiation you have. If this is a boiler worth keeping (less than 15 years old, and in decent shape), replacing/hacking around some of the aquastat controls with a smart economizer, it'll do the hysteresis and high temp adjustments automatically. optimizing the system for the actual heat loads. (eg Intellicon 3250 or Beckett Heat Manager, etc.) These typically let you program the low-limit temp, and takes over from there, squeezing out best efficiency it can muster with the system configuration that it can. It won't fix system design issues or oversized boilers, but double-digit percentage reductions in fuel use are common. And the average operating temp (and standby losses) will be much lower.