Talent Rankings are as followed
[Begginner]
[Intermediate]
[Master]
[Grandmaster]
[Peak]
Active/Passive skill ranking are as followed
{F}
{E}
{D}
{C}
{B}
{A}
{S}
{SS}
{SSS}
The difference in power is about 10x for most skills. The ten times multiplier stacks allow for a clear difference in rank.
In between letter ranks there are Sub stats that do make slight distinctions, for example, a B- Skill is less than a B skill while a B+ skill is superior.