Challenge accepted: I wasn't able to tease out a number more specific than "up to twice as efficient" here

http://jalopnik.com/5490236/the-nuclear-warhead+equipped-ekr...

but it might be decipherable in this PDF:

http://ftp.rta.nato.int/public/pubfulltext/rto/mp/rto-mp-015...

A couple of sources said such a plane can fly up to a few hundred feet up. And another talked about a yacht using WIG:

http://www.yachtboutique.com/Designers/Ekranoplan/Ekranoplan...