If you are doing math on hash keys, then you have tripped into a perl problem: perl treats the number as a string when it is used as a hash key and as a number while doing math. Converting between these two representations is relatively slow.

If you can use mathematical algorithms for doing your statistics that do not involve number-as-hash-key then you might easily achieve a 10X improvement. Especially if the math is done in a module that is implemented with C code.