Take your top 50 artists. For each of these artists, collect the top 20 similar artists (where the artist itself is the #1 most similar). The resulting number of unique artists is your super-eclectic score. You can compute your own score at http://anthony.liekens.net/pub/scripts/last.fm/supereclectic.php
My super-eclectic score is currently
The most similar artists for my profile are Pavement (7), The Replacements (6), Guided by Voices (6), The Decemberists (6), Sonic Youth (5), The Hold Steady (5), The Magnetic Fields (5), Okkervil River (5), Mission of Burma (5), Spoon (5).
For the sake of completeness, I'll note that my regular eclectic score is now up to 95, but I won't post the whole long thing that that script generates.