i've seen people say the Sapphire is better than the Gigabyte and i've also seen it the other-way around, all benchmarks i see are also like this, for the same games, which is weird. like on one benchmark for lets say BF3, it will say Sapphire out-performs Gigabyte, but on other peoples benchmarks its the other way around.
@this lvl benchmarks are kinda irelevant. The only thing that i would take into account is the cooling solutions from each card (witch card makes the lowest noise) and the overclocking headroom of the each card. Basically the cards are going to perform equaly in games if they are clocked @ the same frequency.
The things I would look at as were said before were clock speeds, price, cooling, but also most importantly customer reviews. Other than that they should be identical. The results you were seeing might have been overclocked or with different test setups.