i would definitely recommend going only to 5g after and eighth at the most. the dose-response curve, as with many other psychoactive agents, is not linear. meaning, 7g is not double the effect, but generally exponentially higher. to take the trip up a step i would definitely suggest 5 before jumping to a quarter...the breakthrough could be right around the corner, no need to skip steps on the journey to the top
but really each strain varies in potency pretty decently from my experience. there are mushrooms which seem to be 1.5x more potent than an 'avg cubensis'. and they can't really be differentiated by look alone, some mushrooms acquired can fuckin blow you away at an eighth dosage. perhaps the sources you've had haven't been the strongest. just an idea to keep in mind.
but yeah, if you're fairly resistant, which is a possibility, it could take a quarter or more to give you the breakthrough you're seeking. but i'm willing to bet that 5g will get you there if you're used to an eighth...it seems like double the intensity at least to me, in terms of my subjective analysis of the dose-response curve i experience.