Using the graph that Shiraz posted.
http://www.iceinspace.com.au/forum/s...&postcount=157
It should still take about 6 minutes to become read noise limited, even at ~1.6e-. I based the calculations off of my previous setup was at F/5.7 and a KAF-8300 with a read noise of 8.5e-. It needed 90-120 minutes to reach that point!
Last night I did 10 minute subs with my ICX694 (more sensitive, smaller wells and larger pixels) and it wasn't saturated at the core. Sounds like the gain may be a tad high but you can also throw in some 1-10s subs to tone that down during processing.