Improve Bernoulli benchmarks

[vks]

The changes here should be considered for improving the Bernoulli benchmarks.

[dhardy]

So @pitdicker or @vks do you plan to get to this? I don't know what exactly needs doing myself.

[vks]

I'll probably look into it in a week or two.

[dhardy]

#465 covers this?

[pitdicker]

Yes