more compression = how much gain?

my only real competition around here is currently from a dude that i work with. he drives a 90 integra with no interior and a few simple things done to the engine. anyway... he's working out the issues of acquiring a built b18b block (12.5 comp, ready for a vtec head). anyway. assuming nothing but the raised compression, what kind of gains should i tell him to expect?
yes, we both realize that he's going to need more than just the block, it's his winter project. we're hoping for 300bhp all-motor (maybe using some n2o) by the time all is said and done. i'll try to take some pics of the new parts, car, etc. but it won't be for quite a while.
any input would be appreciated.