if you play my tatic i have x3 mariens before you can even get a reaper in my base, sorted... you will never be able to reaper rush faster than marines rush esk purly due to the tech lab needing time to build, and u need refinerys so you are gonna be behind on unit count
. but by all means its a handy tatic if they aint prepared for it, i sometimes wonder about a mid game x20 reaper rush just to dent their econ, x10 on each base and boom no more builders for them...
liger its cos i let some econ acumilate while i scout about abit (i usualy get 50billions scv's so xD) and ur not attacking till u get to their base so you can que up the buildings keep an eye on he fellas and then do the research if u feel u dont need to micro, simples ^^