In reply to Tomagone: Plenty of decent Sport to be had on the Llanberis Slate. The area known as Australia has lots of lines in the F5 - F6b range. Get the Ground Up guide:
http://www.v12outdoor.com/catalog/product_info.php?products_id=5046
A little further East the Limestone at Trevor Rocks near Llangollen has lots in the requested grades too
http://www.ukclimbing.com/logbook/crag.php?id=427 there is a Rockfax guide that covers these climbs
http://www.rockfax.com/climbing-guides/books/clwyd-limestone-2005/
Along the A55 there are more Limestone sport options, although most of these crags are better for higher grades. Guidebook for these:
http://www.pesdapress.com/Land-Guidebooks/c1_25/p36/A55-Sport-Climbs/produc...
Not sure what the best options are camping wise that put you within walking range of these, but there are certainly sites near Llangollen and Llanberis. The best climbing in the area is of course the Trad, my advice would be to scrimp, save, beg, borrow and piece together a Trad Rack - you've got till next summer so be resourceful.