sunfire and sunpyre have identical powers, though sunpyre, technically, is a continuity error in herself. [sunfire got his powers from his irradiated mother, who was affected by the atom bomb dropped on hiroshima. she died after. leyu (sunpyre) is supposedly his half-sister, meaning they share the same father. but, as their father didn't give shiro his powers, there's no reason for leyu to have the same powers.]
anyway, cassandra nova would be a better match for xavier.
Dust and Sandman have vastly different powers in application, but they're the closest you can get, I suppose.
and neophyte was an acolyte who could merge his molecules with any matter he came in contact with, letting him flow through it and emerge at another point. unlike kitty, he could perform stunts like sticking his arm into a wall, and having it punch someone dozens of feet away along the same wall. also, he once jumped off a balcony into a rainstorm, merging with individual droplets, and reformed one the ground once each drop hit bottom. he's as close as you'll get to shadowcat, though, unless you consider nate grey's pseudo-ability to become intangible.