There is a tendency to get confused over the function of a g-suit. As I posted on the Blue Angel's thread, unless g-suits and the human body have changed drastically since my military days (ok - I KNOW
my body has
) the main function of the suit is to reduce fatigue caused by prolonged and frequent applications of high g, which are commonly experienced in the 'average' day of up to 4 sorties in a fighter. By reducing the effort the body has to generate to combat the g they thus make you less tired. I cannot recall the 'increase' in g-threshold with a suit, but I think it was only of the order of 1-1 1/2g, and I further think that seating the pilot in a prone position has a greater effect on g-threshold, but that is outside my experience.
To further the 'water' line, I seem to recall a Russian experiment with a water filled
cockpit in which up to 20 g were sustainable by a suitably 'oxygenated pilot'.
Light a/c aerobatics rarely have sustained high g, whereas in jet combat it was not unusual to sustain 4-5 g for many seconds - and that is exhausting even with a suit. The BAe Lightning could sustain a 6g turn for a long time (until the fuel ran out) - ok, 2 minutes, then