Are there any tight bits and squeezes and drops involved?
I'm told there is at least one tight bit in Bryn Eglwys (though I'm not sure how tight it is as I've not been to that part of the quarry) and there's also the big wet shaft to abseil.
Ratgoed has a slightly tight bit (though I fit through it reasonably easily) as an alternative to a 60' prussik.
Other slate possibilities for a Corris-based weekend would be Hendre Ddu (wet in places), Minllyn, Gaerwern and Abercorris. Also within reach would be mines at Talybont (Allt y crib, Bwlch Glas, Henfwlch).
Dave