Benw, just been through the same thing, but due to knackered STI's was starting from scratch. I've gone for SRAM STI's, a compact chainset, an Apex 11-32 cassette and matching long cage mech'. This set up works a treat and gives me a super low (by cx standards) gear. Ive been testing it on our local hills, the Cairngorms, and I'm pedalling up some pretty big climbs. Coming from Shimano STI's the double tap systems taking some getting used to, but I really like the mtb feel to the shift – SRAM on the mtb.
Now just need to "up" the training, slight panic setting in!