1400mAh is obviously going to give you better performance than the 1200mAh one so if you are upset at the battery life you are getting on the factory supplied one, it's going to be a worthwhile investment.
As for Hi-Cap, I would think that stood for Hi-Capacity and is more to do with how big the mAh is than what type of battery it is.
Current: iPhone 4
Past: iPhone 3G, iPhone, HTC TyTn II, HTC Touch, Nokia N95, Motorola Z8, Qtek 8500, T-Mobile MDA Vario, SonyEricsson W900i, SPV C550, SonyEricsson K750i, Nokia 9300, I-Mate Jam, C500, Moto V600, SonyEricsson P900, P800, Treo 600, SPV e200, Nokia 1100, Nokia 6230, SonyEricsson K700i, T610, Nokia 7650, SonyEricsson T68, T29, Moto T250, Nokia 8310, Samsung A100, SPV Classic, Moto V50, Nokia 7110, Vodafone EuroTel
Stress is when you wake up screaming and then realise you havent fallen asleep yet!