North Devon is hillier and steeper than South. Compact works well up here. Perhaps consider the new SRAM groupset with big cassette range. I believe a number of entry-level road bikes will be fitted with it for 2011. Will a 10spd mtb cassette work with a road chainset? A lot depends on fitness really. Can you get a demo of different styles? Certini in Saltash could probably provide some demo models.
I'd be wary of the Shimano double/triple shifters. My Tiagra one gave up after 10 months and the mechanic in the shop reckoned he'd seen loads fail when being used as a double. Madison kindly exchanged for a double specific model which felt much smoother to use.
Double 105 on my bike now which feels lovely and crisp compared to Tiagra (which never really felt bad), although with a cross setup (46/36). It does leave me a bit undergeared sometimes, but I find the 36 inner far more useful than the 34tooth I had on my Defy.