Too late now, the house is built, and the baseboards installed. I think the high temperature was a bandaid to poor design, too few feet of baseboard, and maybe poor insulaton.
In my experience, which is about .0001% of Sting's, hot water baseboard systems are designed to run with 180* water.
Maybe this is some new 'economic' measure to use less copper and baseboard length, thereby saving the builder money building the house, at the expense of the homeowner's heat bills.
I see no reason that the KA-4 can't run at 200" but you may have more issues than normal with temperture spikes past the intended high limit.
After a call for heat, after the stoker has filled the bed with burning coal, the water reaches 200*, then the thermostat is satisfied, the circulator stops and the big bed of hot coal has to slowly burn down to an idle fire,, all that extra heat is going to push the boiler temp up. If the running temperature was at 160=180, then there is more room to heat before hitting either a dump zone temp or the PRV's trigger.
Just how big is the oil tank that is being used each month, in this mild weather??