I believe the Pentium P6100 is based off of the older Core 2 Duo CPU core.
The Core i5 would be better since it has a much more efficient architecture than the C2D core. That means if the those CPU were clocked at the same speed, the Core i5 would win.
Just so that you know, the Core i series CPUs in those laptops are from the 1st generation of Core i series CPUs; called Clarkdale (i3 & i5) / Nehalem (i7). The 2nd generation of Core i series CPUs are called Sandy Bridge and they have about 10% better performance at the same clock speed than it's predecessors.