Mr. Sinister isn't a mutant, but he was augmented with his abilities by Apocalypse I think in the 19th century.
Although Illyana was prized by Magneto who wanted to use her as a tool during his term with Hellfire, I don't think she's Omega (her other side of Darkchilde does not count as that was from the remanance during her time in Limbo).
Polaris during her wedding upset showed she is a definite power player. I think she's a good candidate as Omega.
Havok is a destructive powerhouse. I think he's more likely an Omega level than Cyclops.
Genesis, Cable's claimed son was a telepath that never truly amazed me. He was tougher looking while posing as Mr. Tolliver. I doubt he's an Omega.
Selene is definitely an Omega since the beginning. She has so much versatility, power, and control of her powers.
Normally a person lower than a telepath would not be considered a good candidate for Omega, but Mastermind has tricked a slew of X-Men post-Dark Phoenix rather easily on thinking of her resurrection (even tricked Wolverine's senses) and even greatly deceived Rachel/Phoenix thinking he's Franklin Richards. He's a definite good candidate.
Rogue possibly, but only on the term that she's capable of retaining the abilities she absorbs permanently.
Other names that come to mine are Gamemaster, Sienna Blaze, Jamie Braddock, Exile's Mimic, Exodus, and Meggan.
Possibly, but unless he's demonstrated large scale changes in more recent comics, my familiarity with him says he's not. Sure, he's harder to kill now and has far more control, but what exactly is the radius for his attacks? They are usually for shorter distances (or focused medium distance).
but would that(range) have a bearing on his mutation level? his power at close range is extremely effective, and he has so much control over his powers as they are now. if he isn't omega level i'd say he's pretty darn close...
yeah i'd say cyclops and havok are pretty even except it seems like havok can chanel more energy at once cause it comes out of his hands and it is easier for him
Their attacks are far different and Havok's have been used as a source for the likes of the Living Monolith and Plasma. Cyclops is concussive, which although is strong, doesn't guarantee an Omega level (I think Omega usually referring to affecting large scale area).
I'm not familiar with Elixir and perhaps my interpretation is different on the term of Omega Level, but when I see Cyclops doing huge scale actions, he is usually doing this as an extension through another, such as Jean, Polaris, and Nightcrawler.
A character does a special feat when complimented with another. Example: Cyclops with Nightcrawler and Jean (actually, I think it may have been Phoenix) combined sent a group of godlings (I say godlings in reference to power not by proclaimed title) to the afterlife, or something like that (they were meant to die, but an accident occurred that had them stuck in a midbetween state).
Captain Britain is suppose to be the strongest of the dimensional Britain corps., but even then, unless he's gotten a recent power boost I would say no. During his time with Excalibur, I found his character the least inspiring. Strengthwise, Meggan seemed to do more than him.
I think it's in reference to being extremely high in one or a number of categories beyond the norm/average mutant of similar abilities, such as strength, telepathy, etc. For Selene, I also felt based on variety.
ok... well as for wide range damage, cyclops has only (to my knowledge) removed his visor twice to use a maximum strength blast, and neither was extended by anyone else...
its just that (imo), he's too uptight and too controlled to really cut loose...
Prof. X (no, many limits to his powers)
Cable (Maybe)
Nate (Maybe)
Jean (Yes)
Madelyne(Is an clone of Jean, so yes)
Rachel (Probably, although doesn't seem as powerful as her mother)
Magneto (No)
Joseph (no)
Xorn 1 (?)
Xorn 2 (?)
Kid Omega (Yes)
Gambit (potentially, like you said)
Shadow King (No)
Apoc (No)
Weapon XV (No)
Fantomex (No)
Wanda Maximoff (No)
Hyperstorm (Yes)
Stryfe (Maybe)
Sinister (He is not an mutant)
Cassandra Nova (No)
Illyana Rasputin (No)
Mikhail Rasputin (No)
Holocaust (No)
Legion (Maybe)
Proteus (No)
Polaris (No)
Havok (No)
Cyke (No)
Deapdool (Deadpool is not an mutant)
Cable's Son (No)
Selene (No, needs to drain people if she wants to live)
mastermind (no)
Rogue (no)