I personally used 9B 02 00 00 value, which is a 33.3% increase.
I've read most of the topics concerning this subject and most agree that 25% is too little, but going 50% means you wont get to high levels by the time they actually matter, that is not untill the very end of the game. So in the end i decided to go with 33.3%. I will report my experience in a week or two.