I recently cast on for the Whisper cardigan, using the recommended needle size of 4.5mm. Then I ripped it, and cast on using 4mm, and knit something like 40 rows. Then I stopped lying to myself, ripped it, and cast on with 3.5mm needles.
As a bonus, this lets me use my new Chiaogoo spins! Very impressed so far, though there is a bit of a snagging problem with the joints sometimes. The swivel is great though and I love the tips themselves.0