We don't have enough information. It would depend on how you define "speedup". It would also depend on whether in the "core 2" example, did they run sequentially? Did they run interleaved and the time listed is how long each thread took by itself?
Personally, I don't see what difference it makes how long each thread took - what matters is how long the total job took. If thread 1 starts and runs to completion before thread 2 can start, then you really haven't saved anything.
Multi-threading isn't a panacea. It won't always save you time. Think about the old saying that "Nine women can't have a baby in one month". Some tasks can't be split up, so no matter how many threads you have, you won't save any time.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors