One thing I thought of while reading the discussion was the pronunciation of the 'ch' in various languages (because I'm a linguistics nerd, particularly with Old English and Insular Celtic). I found a link: http://dictionary.reference.com/browse/arch that I found interesting; it implies that, while the prefix 'arch-' comes from Latin, in Old and Middle English it was pronounced as a hard 'c' (much like the Scots Gaelic 'loch', as someone mentioned earlier). Old English was a Germanic language, spoken in an area surrounded by Brythonic- and Goidelic Celtic-speaking people, so it is entirely possible that the hard ch comes from one of those directions.This obviously has no real bearing on the pronunciation of a Modern English word, since Old English is nearly unrecognizable to a modern speaker; it certainly has no bearing on regional dialects. But I found it an interesting idea nonetheless.

And in Ancient Latin and Greek, the "C" always had a hard sound, like a "K". For example Caesar was not pronounced See-sar, but Kai-sar (and is the origin of the the German title Kaiser). Celtic is pronounced Keltik, not Seltik. So there too, the even older pronunciation would have been ark, not arch.

It's tomato sauce not ketchup I tell yah.

And in Ancient Latin and Greek, the "C" always had a hard sound, like a "K". For example Caesar was not pronounced See-sar, but Kai-sar (and is the origin of the the German title Kaiser). Celtic is pronounced Keltik, not Seltik. So there too, the even older pronunciation would have been ark, not arch.