Hi John,
I remember there was some discussion on the ARAS forum about the long tail of warm pixels seen in cameras with Sony CCD which seems to have got progressively worse with each generation.
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1919&p=9871
I recently saw an article somewhere which suggested this was a characteristic of CCD with anti-blooming, a connection had not been aware of before.
Discounting these, the noise figure of these CCD is very good though and they seem to respond well to dark subtraction.
Running at a lower temperature might help. I run my similar ATK428 at -10C all the year round.
Robin