Quoted from developer for Nexus 6 with 5.1:
"the device is now running full quad-core mode all the time which helps tremendously because the Kernel task scheduler can distribute the workload through all these cores so you'll get the perception that the device is not hanging anymore."
I'm becoming increasing interested, I know the S6 and M9 are around the corner but I want to keep the N6 in the mix.