this is the approach that I have taken to determine optimal ISO and sub times (using a Canon 400D):
http://www.iceinspace.com.au/forum/s...d.php?t=106775
and again with a Canon 1000D:
http://www.iceinspace.com.au/forum/s...d.php?t=108354
I have have just been through this entire process again, as I've just completed a regulated cooling mod to the 1000D (above) and also a 450D and have followed the same approach to determine optimal sub/ISO settings under regulated cooling conditions.