Understood. At no stage was it was my intention to suggest that you should use Math::GMPz instead of Math::Int128 - I was merely querying the speed of Math::Int128 (whose basic math operations seem to be about 3 times slower than need be), and using Math::GMPz for benchmark comparisons.
Apologies for my part in forcing that upon you - though that was never my intention. (I know very well how annoying it is to be taken to task over matters that are irrelevant to the task at hand.)