In reply to Jon Stewart:
In N Wales, in addition to the slate (special mention for Australia and Peppermint Slab in the grade range of interest), the A55 crags in also have a fair amount of good quality bolted slabs in the F5 and F6 ranges. Penmaen Head, Trench Wall and The Gallery are often off vertical and technical but mainly/entirely too steep to be classed as slab. However There are good, genuinely slabby, routes at Castle Inn Quarry. Penmaenbach Quarry has many good slab climbs in this grade range and there are other good slab climbs at Creigiau Cigfran (Llanfairfechan). Penmaen West Quarry also has good bolted slabs but unfortunately climbing is currently banned there.