Eegah, Jerry's "school play" description was spot on.
George's girlfriend in The Hamptons was played by Melora Walters, most famous for her appearances in the films of Paul Thomas Anderson. She is certainly an attractive woman, but I wouldn't put her at the top of the list of George Costanza girlfriends who were out of his league.
Personally I would say it is a tossup between DeeDee Pfeiffer from The Opposite, or Chelsea Noble from The English Patient.
Guess I have a thing for redheads. I forgot about DeeDee Pfeiffer (Michelle's sister, right?). Yeah, quite out of the league, although she was attracted to the Opposite George, so there's that caveat.
I didn't count Chelsea Noble, since her attraction to George (and his doppelganger) was so improbable and incongruent even to George that it became the focus of the story line.
It only bugs me, in this and any other sitcom, when there's no explanation, or even comment, on the very unequally yoked.