genre/book-related question

Because we had a - well... not an argument, really, but we couldn't actually agree and had to table the discussion to move on to other questions - a debate about the difference between science fiction and speculative fiction last night while discussing Oryx & Crake. Two people who are most emphatically not sci-fi fans insisted that the book belongs in that genre.

To me, Oryx & Crake is speculative fiction. Sci-fi is... a subset of speculative fiction, maybe? No, that's not right... maybe it's a sibling? Related, but not the same thing.

When I think about my own personal definition, sci-fi usually has something that's not in sync with science and the physical world as we know it. Crazy space, time, or physics, weird powers, something wildly different than our current world. Whereas speculative fiction takes our world and extrapolates, posits a What if?

Thoughts? How do you define sci-fi? Speculative fiction?