In reply to 3kidsandanorton:
Firstly, midges don't go to bed until it's proper dark.
Secondly, the guide Andy mentions is your best bet, but still not very useful, giving (mostly) only British technical grades (range 3a-5c).
Thirdly, I have visited the cliffs and come away thoroughly uninspired (even though I love Torridonian sandstone and sea cliffs). The rock is a bit greasy and rotten.
Probably better to have a look on a wet day when climbing isn't an option.