Thanks everyone for the input. Rightly or wrongly I've decided to get the E-M1, on the basis that it offers me features I value now (bigger/sharper EVF, PDAF, better high ISO performance, better IBIS, improved handling etc) and the deal was really good (£150 off a lens, meaning I got the 25mm 1.8 for barely more than £100, plus a free HLD-7, which I will sell).
Talking of which, if anyone in the UK wants a new, unused, unopened, Olympus UK-supplied HLD-7, please PM me as one will soon be available...