Since the SX website states that the read noise for your camera is 'Less than 9 electrons RMS - typically ONLY 7 electrons! ', I suggest sticking with 10 minute exposures rather than shortening them to 5 minutes. Having said that, from my limited experience, the length of exposure may vary depending on the target - with brighter targets like the Carina shorter subs are the way to go, while for dimmer stuff longer subs work better.
In the end - the only way to know for sure what works in your location and with your imaging train is to do say 1 hr exposure of the same target and on the same night with 10m and 5m subs and compare - standard deviation of the background and areas of interest, SNR with PI script etc.
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