Right off the bat, the Brahms Variations came to my mind too, although i did hear someone say liszt's don juan fantasy...i try to reply only to stuff i know about, and this is my expertise...Don Juan would be a great piece, probably better than la camp or hamelin's transcription thereof. THe problem with don juan is that it wouldnt test just technicality because of the duetto middle part; and if this were shearly a technical competition the musicality of the piece should not come into question,only the ability to execute unflinchingly and with little exertion. Thus, a set of variations might not be ideal because each variation also requires a different mood or tone, even though a lot of technical feats are encompassed. Thus, thinking of a shearly technical piece that has little musical bearing,i might suggest Islamey, as volume and mood-wise it isnt as challenging as even the most shallow rach work. therefore, rach is out, liszt is out, chopin...out. Although unreasonable, i might suggest the OC, and seeing as how it is four hours of blistering technical ass-rammery, it is dense, and just understanding it is troublesome, i might recommend that. But for difficulty technically if musicality is only a result of viruosic expression, then i might also suggest the second prokoffiev concerto, the rach 2 sonata, liszts norma variations or, yes, islamey...i like the brahms variation way too much to reduce it to only technical stature