Rudds,
I think this has come up once or twice before. Try a search using Iceland (and also Faroe Islands) for some usefult tips. I managed to find
this thread which may be helpful.
It would also be worth having a read of 2 Donkeys' story of how he flew his TB20 to the USA via Iceland - you can donwload a PDF of the account from
here.
Do you have an IR? if not then you'll be restricted to below FL55 once you get to the Icelandic FIR.
Brooklands