It might be. We've considered having it be configurable before. There are just a lot of implications in changing the value; for example, it affects the memory footprint of the server, it affects how much data gets read in to memory per read() call on a file bucket (which might alter the decision of whether read() or mmap() is preferable, for example), it affects how well the data fits into memory pages, and it affects how much data is buffered in one block for the scenarios you described. There are probably others I'm not thinking of right now, too. Lots of different axes that must be considered when trying to pick an optimal value. But still, if you want to make it configurable, go right ahead. :)
Right, I saw all the things it affected which was precisely why I wondered why it wasn't made configurable. I can see perhaps protecting users from themselves, but other parts of Apache2 doesn't really follow that. The WindowSize config option in mod_deflate would be a very bad idea to change away from the default of 15, for example. Anyway, I will go play a bit with the bucket size on 64-bit boxes.
-Rasmus
