You certainly can't "speed read" on a Kobo; the page turns are glacial. This doesn't impede "real" reading.
Since I've owned my Kindle 2, there have been two batches of firmware upgrades, each shortening the page turn. It's reasonably "instant" with 2.5.3 so, yes, you could "speed read" with a Kindle 2.
My understanding is no other mainstream device -- any of the Sony, Aztak and other e-reader players -- deliver "fast" page turns ... but fast enough for "real" reading, however.
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