I was dropping some people out to Heathrow and actually saw Clipper 103 take-off from LHR that night. Weather wise I seem to remember that a south-westerly gale was blowing in. This probably necessitated the northerly routing.
In my trips across the pond I have been on a London - Boston that went out over Macrihanish and a London - Toronto that went north from Glasgow. Furtherest north was a London - Vancover which eventually flew across northern Greenland.
Quickest and bumpiest eastbound was a BA 747 MIA - LHR done in something like 6 hours - we must have been in the jetstream the whole way - a real rollar coaster, seat belts on all the way. All went well to OCK then we spent at least an hour in the hold at OCK as everybody else from US had arrived together. Mayhem in the baggage hall as a result.