The Sunset system is based on the USDA hardiness zones map, but more sophisticated in that it breaks up the USDA zones (basically frost-hardiness only) into much subtler divisions that take account of other climate factors. I've only seen maps applying the overall USDA zones to Europe - and on those, then the Costa Blanca is indeed Zone 10. The various versions of European maps with zones based on the USDA bands do disagree with each other to some extent, but Costa Blanca always seems to be Zone 10. The only disagreement there seems to be about how far inland this mild zone extends.