I'd suggest running it at Gain 200 Alex. Going further than that doesn't appear to have any real benefit and it should allow you to get the most out of your two minute exposures.
If two minutes is the limit on what your mount and tracking can reliably do then that should be your maximum
That is something else that sets limits, there is no point in going for that 5 minute exposure to get a nice background if all your stars are eggs
