I just got to this battle and finished it. It took me an hour and 1/2 to beat it. I had in first squad ramza agrias and a summoner. Second was a lancer and white mage. I got lucky and stopped gaf at the start and broke his weapon. I killed him but I was taking lots of damage. Summoner was extreamly useful with fariy. My other party just ran like hell towards my first and we played defense from there. Time mages are the only healers so take them out fast.