Galaxy S5 Broadband LTE-A: 5.1" 1440p previous gen AMOLED + 28 nm HPm Snapdragon 805,
pretty much the same result (98.9%) as
Galaxy S6: 5.1" 1440p current gen AMOLED + 14 nm LPE Exynos 7420.
S5 LTE-A has ~7.7% bigger battery (10.78 Whr vs 10.01 Whr).
So S6 is only ~8.9% more efficient in this...