Yeah I use a standard cooling level of -10C, as up here in QLD I can attain that even on warm summer nights, like last night where at midnight it was still 25C and 80% humidity
The 1600 has no problem handling that though, and I'm not convinced that the increased thermal noise from going that much deeper is significant, given the number of subs I (would) like to chase... the 1600 is pretty low noise by any standard.