i agree that the true beast of the WG consist of 11 people, and they are:

sengoku, garp, kong, the 5 gorousei, and the 3 admirals. we have seen the 3 admirals and their ability. we have seen a bit from garp and sengoku, and i beleive we have only scene fraction of their powwer. im sure kong is a monster, he has to be at least as strong as garp and sengoku. the gorousei are interesting, i cant wait to see them, maybe they have some special type of fruit powers.

as far as the yonkou. i would say that they are the best in the NW. im sure some of the levl 6 prisoners can hang one on one for a bit, but the yonkou are like generals of their areas and are repected as such.

dragon just looks like he is a beast, so it would be safe to say he is just as strong as a yonkou or WG top member in respect and strength