Don't even think about maxing out Luck, it will just take too damn long. Greater Sphere/Earth Eater are a complete pain since they counter nearly every attack. It's not impossible to optimise your stats to a point whereby you can have 255 in all stats except Luck, which you can safely have around 160 odd without too much hastle, and end up with about 80k life. People will however insist that it's better to have lower HP and use a combo of Auto-Protect/Auto-Shell/Defend. Of course it's the Heavy Tank versus the Titanium-Armoured Shrimp. Personally I'd have the Tank.