In reply to Formerly Known as Pylon King:
I think the BMC guides have done a good job on this, giving all sorts of silly combinations of grades like V2 (E2 6a) and E3 6b (highball V4) depending on whether it's
more bouldery or
more traddy.
I just think that everyone's standards are a bit different when it comes to what's a good little highball rather than a dangerous solo, so it pays to have a variety of information.
For example, I think that Pedlar's Slab, Arete and Rib are all great solos, but Punklet is a good lead (I have soloed it, the easier way, and was very scarey). You can't tell be the grades, particularly.