I'm surprised you got such a high (11%) boost. I would not expect branch prediction issues from your code to have much of an effect in Python because the Python interpreter itself naturally introduces 10x as many branches under the hood as the code it interprets.
guess: the branches in the python VM are more accurately predicted than branch on the data. The data is going to be random and thus unpredictable, but the branches in the VM are probably pretty predictable.
Python if statements will branch on very few processor instructions in the VM; so I don't think branch prediction of the processor is able to predict different Python if's — they're all the same to it.
Well, that... and even simple Python VM instructions tend to take dozens of insns to execute.
