1) 2500 of any type does not have hyperthreading.
It is the 2600 that has hyperthreading, a higher clock, and a larger cache.
the 2400 has a lower clock.
2) Anandtech had a engineering sample. Production specks could change.
3) Here is the link: http://www.anandtech.com/show/3871/the-sandy-bridge-pre...
^ Yep, Intel gave Anandtech an engineering sample of the i5-2400, according to the article, and it had hyperthreading enabled but no working turbo. If you want working HT on a quad-core Sandy Bridge that you can actually buy, you'll need to get either the 2600K or 2600. However it appears the hardware for HT exists on the 2500, 2500K and 2400 models at least. I wonder if some smart mobo OEM will find a way to "unlock" the HT hardware ..