In reply to TobyA:
> Does anyone not just place a runner or two whilst going up the crack? Is it really that impossible?
Yes, I did. Both times I've done it (see spoiler).
If you're stable, then it would be possible, but pumpy to place more. I think jamming it would be awkward, the corner would be a bit of a squeeze, but it might work.
Sorry if repeat mention, but
Brooks' Layback (HS 4b) is a similar shape but easier proposition.
For me I reckon Altar crack generated a similar pump to right unconquerable, but over a shorter distance and felt less reversible.
Top outs easier though.