I find it funny that this thread is littered with postings that indicate the F last fits large on most people, with those with wide width and/or high instep being the exception, but people are still going with their direct conversion from their normal UK/US sizes. I have posted a conversion chart earlier and if you compile even just a handful of sizing posted and study that chart closely, you can work out a fairly accurate correlation between the F last and UK/US sizes. And yes, the F last do, FOR MOST PEOPLE, fits larger.
How does the F last compare to the New Peter last? If I wear a 43 in New Peter (I have this one), should I go down to a 42.5 in F or stay 43? I've been kinda lusting after these in F last lately: