Ed Zubrow:
>The piece then concludes with a fugue; in my limited experience, I don't
>know of other Variations that use four and a half minute fugues (as opposed
>to canons).
I can't speak to time, but let me propose the Bach Goldbergs, the Brahms
Variations on a Theme of Paganini, and the Reger Variations on a Theme of
Mozart.
Steve Schwartz