In reply to Welsh Kate:
I seem to remember ages ago Jerry Moffat said it was about E5 5c, but I can't provide a reference or source other than my addled memory. I think it was an interview in High c1992, it stuck in my mind as he said it reflected a lot of identical moves with only the lighting conductor to clip into.
Edit, slab happy might be more accurate above.
Post edited at 10:50