IOMX
I'd have to disagree about 1 hour to the centre of London from London Gatwick. Gatwick Express can be less than 35 minutes to Victoria. And you can take a very economical option to Blackfriars or London Bridge. It can be as quick as 42 minutes to either stop.
As an aside, apart from Heathrow express ( and not really relevant for this conversation as no service to LHR ex IOM obviously), for a fast route into central London, Gatwick is super. Interestingly, easyJet from Gatwick is best all round for me. Reasons being pricing of easyJet (competitive), and with easyJet Plus you get priority lane passport control and there is never more than 2/3 in the queue even at busy times... I cannot fault easyJet, they in my opinion provide a great service. Besides I prefer to fly on a jet over a turboprop any day....