My experience about G
With a G suit, i was able to support, in the same time in test flight :
20 seconde to go to 4g, then go to 5g stay 20sec at 5, then 6g 20 secondes at 6, then 7g , 20 secondes at 7 g. At least more than one MINUTE above 5g without a blackout.
The g tolerence depends on pilot healt and most important thing, on with rate the G grows. With a good trainning ( not a "competitors trainning") a pilot can be conscious above 7g without any probleme.
The only probleme is about he fuel. With a fighter, a modern one, to keep 7 g and more constants, you need full AB. So the flight is very short.
I ve made some flight of this kind, in low altitude. The dogfight was between 5 to 7G during most of the time (certainly above 5 minutes) but the total flight time was only 15 minutes from take off to land.