Closed or Open Cooling System?

[mclairmo]

I am about to add a coolant recovery tank (billet cylinder type) and it appears to be a closed system tank. The coolant flows from the radiator into the recovery tank from a nipple at the bottom of the recovery tank and thus (I assume), that when a vacuum forms in the radiator, it will suck coolant from the recovery tank back into the radiator. My cap has two seals on it. My question is what is the advantage of a closed system? Will it help my engine run cooler at all? Also, what is the advantage of a higher rated radiator cap? I have several on hand (even a Griffin 24 lb racing cap) and wondering if higher pressure is better for cooling? I know that the higher caps increase system pressure which increases boiling point but will this help me run cooler or just prevent earlier boil over?