>> The simpler your scene is, the less memory it takes as a whole, and
>> therefore the more of it can be kept in the CPU caches; as a result, the
>> CPU spends more time doing actual work than waiting for main memory
>> operations to complete.
>
> Shouldn't matter here because in both cases the object data is the same.

I don't think the object data is the same, in one case you have a 
difference object with N+1 child objects, in the other one you have N 
nested difference objects, each with 2 objects.

My suspicion is the nested objects cause a lot more "memory" type work 
for the processor during rendering (reading pointers, transform data 
etc) and as such even though the CPU is at "100%" it's having an easy 
time waiting for slow memory operations to complete.

How do the CPU temperatures vary as you change the number of particles - 
are they much closer with just 1 or 2 particles?

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