Great report.
A bit of trivia. The Hilton T4 was originally built by the now-defunct BAA (the previous British Airports Authority before it was privatised) and was branded the "Sterling", which was BAA's short-lived luxury airport hotel brand. The Sofitel Gatwick was part of the same chain which accounts for its similar external experience. Both hotels had direct access to T4 and the North Terminal respectively which was something of an innovation in the UK when they opened.
http://hiltonlondonheathrow.blogspot.co.uk/2013/