This release is reported to be around 60 ELO stronger than Stockfish 6, but that is only when playing against itself, not other engines. The SMP algorithm has been changed from YBW to Lazy SMP, whatever that means; I have no idea.
The download comes with the 32-bit, 64-bit, 64-bit bmi2 and 64-bit popcnt versions. As for the last two versions, I have no idea what they are either...something to do with each version being optimized for a particular type of hardware.
Bmi2 (which will not run on my laptop) is the fastest but only runs on recent Haswell CPUs. Again, I have no idea what the Haswell CPU is.
The popcnt version is supposed to be faster that the x64 version. It is recommended that if you have a new computer try the bmi2 first. If it doesn't work then go to the popcnt version, then the plain 64-bit and finally, the 32-bit version.
Download direct from the site HERE.