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You can't "burn" anti-freeze in a hot water heating system and if you set the hi limit too low your heating system won't keep your house warm on the coldest days. 190 is typical for systems with copper baseboard radiation. Other types of radiation typically have a lower design temp.
It depends on the system design. 160 could be adequate if that's what the system was designed for. 190 isn't too hot but it may not be necessary to run the boiler at that temp which could be slightly less efficient if the system was designed for a lower temp. You'll know if the temp is too low if you can't keep your house warm on the coldest days.