Thanks for the very comprehensive reply - the next port of call after Reykjavik is ÍSAFJÖRÐUR !
After considering all the very informative replies in here ( may thanks ) , decided to do the Fred excursions on this occasion . For the costs involved , simply wasn't worth the costs / hassle if things didn't go to plan , even if the chances of that happening were remote .
Also decided to do the ice fjord trip after all the recommendations in here .
Cheers ,
Pete