Graham.
Let's define the required accuracy.
"Tallboy and Grand Slam required to be dropped within 150 yards of the target from 20,000 ft.
617 Sqn with SABS achieved 170 yards over the period June-August 1944, improving to 125 yards in February-March 1945."
source:
http://www.geocities.com/skidaddy20000/Air-Bomber.html
"Oboe was extremely accurate, with an error radius of about 110 meters (120 yards) at a range of 400 kilometers (250 miles), about as good as optical bombsights."
source:
http://en.wikipedia.org/wiki/Oboe_%28navigation%29
I understand that Oboe was not a bombsight. The effect of wind and speed and length of drop would have to be computed separately, but was well within the technical capabilities of the time (SABS and Norden).
Furthermore by December 1944 there would have been time to set up Oboe cat and mouse sites in Holland and France to extend Oboe coverage well beyond Berlin at 20,000 ft.
It is not clear whether in December 1944, 617 Sqn had achieved the required accuracy.
Tony