A buffer would be a band-aid (and an expensive one, if going with a BoilerBuddy or ErgoMax). Right-sizing the boiler is a much better approach, but as pointed out previously, even with the -050 it'll still short-cycle on the fin-tube zones unless you marry them into a single zone or increase the radiation on each of the small zones.
At 180F out it's probably getting ~87% combustion efficiency. If it's running 180F out at 37% of the -100's max fire that's (0.37 x 0.87 x 100K-in= ) ~32KBTU/hr, and you're already at the highest temperature that the PEX is rated for. If your radiation can't take anywhere near the full output of the boiler without melting, it's dead-certain that it's the wrong boiler, eh? ;-)
At 180F out it's probably getting ~87% combustion efficiency. If it's running 180F out at 37% of the -100's max fire that's (0.37 x 0.87 x 100K-in= ) ~32KBTU/hr, and you're already at the highest temperature that the PEX is rated for. If your radiation can't take anywhere near the full output of the boiler without melting, it's dead-certain that it's the wrong boiler, eh? ;-)