Lots of non-sea island cotton is labelled "sea island" or "sea island quality" as a marketing ploy. I have a sea island shirt, it's nice but it wrinkles like hell, so I don't bother with sea island anything anymore.
Egyptian comes in many varieties from junk to fantastic. I have a pair of Baldessarini pants that are promimently labelled "Egyptian Cotton" on the inside. The fabric has an incredible lustre, and softness like sea island, but is not as wrinkly as sea island.
That said, its pretty damn hard to make a decision based on buzzwords that people are throwing around. See and feel the fabrics, then decide.