All I can say, is that when you bring the guns of a heavy first rate up against a galleon, the galleon tends to well....melt

I don't know if I would reccomend taking an evenly matched fleet of 5th rates vs. a fleet of galleons though unless your naval control and tactics are exceptional. Galleons are closer to a 3rd rate in terms of firepower, so unless you really out maneuver them, you'll be floating on a board before the day is through.