Well, just got back. Couldn't convince my girlfriend to take the U-bahn out as far as Tegel for a whisky shop, but did manage "Wein und Whisky" (really ought to be "Whisky und mehr whisky" as there was no wine in the shop). A great shop with loads of bottlings, OBs and some very rare IBs. Most things struck me as on a par, pricewise, with home. Some bottles were maybe 20% cheaper: all bar a bottle of Blanton's which, at €25 was too much of a bargain to leave.
The person in the shop was very helpful and spoke excellent English (he appreciated that my girlfriend was the linguist and her whisky vocab was limited in English, let alone German!) All round the shop gets my ringing endorsement!
(As an aside for anyone else going to visit: a surprisingly large number of bars have half a dozen or so single malts and the big department stores (especially KaDeWe) have very impressive selections. For anyone that is interested: there is also a tremendous number of cigar shops!)