CCRL 40/40 Rating List - Custom engine selection
723446 games played by 1896 programs, run by 19 testers
Ponder off, General books (up to 12 moves), 3-4-5 piece EGTB
Time control: Equivalent to 40 moves in 40 minutes on Athlon 64 X2 4600+ (2.4 GHz), about 15 minutes on a modern Intel CPU.
Computed on July 1, 2017 with Bayeselo based on 723'446 games
Tested by CCRL team, 2005-2017, http://computerchess.org.uk/ccrl/4040/
Rank Engine Elo + - Score AvOp Games
1 Booot 6.2 64-bit 4CPU 3221 +25 -24 44.7% +33.8 456
Booot 6.1 64-bit 4CPU 3178 +21 -21 39.5% +63.9 632
If you want 4 CPU and 1 CPU ratings to be comparable (which is important to measure SMP scaling), you should really do more 4 CPU vs 1 CPU. Things like Engine A 4 CPU vs. Engine B 2 CPU, etc.
Without those missing links, BayesElo (or Ordo) have very little information to make the 4 and 1 cpu ratings coherent.
Theory and practice sometimes clash. And when that happens, theory loses. Every single time.