Good question. I want to add that, we don't use, most of the time, "가히" compared to "제법" But you can see this in the formal writing. If one says in an everyday conversation saying, "지금의 상황은 가히 절망적이다", then probably some people would feel that the speaker is a weirdo.

가히 and 제법 are fairly similar in meaning but quite different in usage and feel. * 가히 = truly; enough in certain quality. It sounds thoughtful and literary, and is almost never used in conversation. Colloquially, we say 꽤, 꽤나, or 상당히 in place of 가히. * 제법 = quite. It describes how some quality is surprisingly pronounced, usually as you first notice it.. It has a light and colloquial feel, and thus commonly heard in conversation. It also has a condescending tone, so you can't use it to comment on someone superior to you. Examples: - 그의 인생은 가히 영웅적이었다고 하겠다 = It's not an exaggeration to say he's had a heroic life. - 지금의 상황은 가히 절망적이다 = The present situation is truly hopeless. - 날씨가 제법 춥네 = Hey, I'll be damned - it's cold. - 아이가 이제 제법 말을 한다 = The child is really getting the hang of talking now.

가히 : most likely, almost (a little below the baseline) 제법 : fairly, considerably (a little above the baseline)