the specs are per cpu, so yes it is 1.67 GHz per cpu, it's 32-bit until the next launch (core 2 duo), and the regular centrino is single core, but if you get the single core, make sure you grab one with the new sticker on it that looks like the centrino duo sticker. it is a better cpu than the pentium m generally, so get one of those two. turions aren't recommended, but if you absolutely HAVE to have 64-bit, that would be the immediate answer.
centrinos outperform turions, but 64-bit is only on turions as of now. the choice is yours.