>> The basic claim that I'm making wrt to this benchmark is that there may 
>> be a significant impact on performance with changing the block size, 
>> thus this is worth investigating. I think this claim is quite safe, 
>> even if the benchmark is not the best possible.
>
> Well, you went straight to making it something adjustable at run time.
What I really did was to go straight to asking the question:-)
Up to now I have two answers, or really caveats:
 - a varying blocksize implementation should have minimum effects   on performance for user of the default settings.
 - the said benchmark may not be that meaningful, so the performance   impact is to be accessed more thoroughly.
> And I don't see that as being warranted at this point. But further 
> benchmarks sound like a good idea.
Yep. A 10% potential performance impact looks worth the investigation.
-- 
Fabien.