If at all possible, try to get a week 26 chip. They're really OCing a lot better than the previous ones. Guys are getting 3.6GHz on air with the same amount of voltage a lot of us are using to get 3.2/3.3GHz stable. Way better chips.
That said I've got a week 23 and from what I've been reading ...
Week 23 < Week 24 < Week 25 < Week 26
Unfortunately I don't think most big online stores will let you cherry pick procs.
Just an FYI.
EDIT: I just read another guys post and his week 26 E6600 is not quite as impressive as some others, but it is still better than any week 23 I've seen.
That said I've got a week 23 and from what I've been reading ...
Week 23 < Week 24 < Week 25 < Week 26
Unfortunately I don't think most big online stores will let you cherry pick procs.
Just an FYI.
EDIT: I just read another guys post and his week 26 E6600 is not quite as impressive as some others, but it is still better than any week 23 I've seen.