What speed (as in metronome setting) would you play this at? Nearly all midi or mp3 files I listened too play this piece way too fast -to my liking anyway. Besides, the composer himself indicates 'Lent et douloureux' which literally translated means 'slow and painful'.

You may want to check Reinbert de Leeuw's interpretations. You'll find mp3s if you look. Info about Reinbert de Leeuw is at
http://www.af.lu.se/~fogwall/reinbert.html

I would take it at about crotchet = 80. It isn't to be as slow as Reinbert took it. THat leaves the listener bored and waiting for something more interesting to happen.