Mutants can be classed in several different ways, both by degree of power and physical strength. Marvel Comics does not have a written or concrete standard for measuring mutant strength. This section is merely a Guide to help with character creation and approvals, though someclassifications may (and already have) found their way IC.
Normal: Can press between 75 - 130lb
Athlete: Can press between 175 - 350lb
Peak Human: Can press between double their body weight to 800lb
Enhanced Human: Can press between 800lb - 2 tons
Class 10: Between 2 - 10 tons
Class 25: Between 10 - 25 tons
Class 50: Between 25 - 50 tons
Class 75: Between 50 - 75 tons
Class 90: Between 75 - 90 tons
Class 100: Between 90 - 100 tons
Incalculable: A person capable of lifting far in excess of 100 tons with no given upper limit
(Heres where it gets sketchy, this is info I've compiled from various sites and comic references, this is an opinion, though for now is CFX's standard. If you have solid info that proves, disproves or otherwise changes what is here, please share.)
Alpha Class: Mutants with powerful mutations who exhibit a strong degree of control over said abilities. (Level of power typical to an X-Man)
Beta Class: Mutants with powers that are relatively harmless or unaffecting.
Epsilon-Delta Class: Persons with latent mutant genes, or highly unnoticable abilitys.
Omega Class: "Mutants with the ability (or potential) to exist beyond the physical realm and consciously explore the mystical. Immortality is also a possibility, but not a requirement. Being able to control matter on the sub-molecular scale also seems to be a requirement." From wikipedia, again, indesputable, but until something stronger is made available, this is the standard.