In reply to DWS gibraltar:
As its your 50th its got to be special and assume that you can be flexible about when you celebrate given that Dec is your target month
Pabbay Mingulay - as it it right out there but you need a load of mates to come along
Lunday - Away from it all experience and great accomodation if your rent a landmark trust cottage (it is your 50th so you can afford it) but not great in December
Yosemite but you need more time than you seem to have
Arapiles Grampians and Blue Montains - but you need more time than you seem to have
Verdun - And get a Gite
Lofoten - a special place I am still not 100% sure that the climbing is the best ever but its a great place to go for something a bit different - but probably no good in December lol
South Africa - Waterfall Boven book your flights early to get a good price and there are bungalows for approx 800 rand about £33 per night for 4 folks at tranquilitas above the crag
http://www.tranquilitas.com/
Pembroke - get a cottage as its your 50th rather than slumming it. Coastal cottages of pembrokeshire do nice ones
Go round the south West and tick off the classics
Of those options I think I would probably go for Lundy for a 50th as you can completely wind down as you never get in a car