> As for marhsalled data and pyc compatibility, yes that is important to
> consider.

The problem is also that with the 30-bit digit patch, some Python will use 15 
bits whereas some other will use 30 bits. The base in marshal should be the 
same in both cases.

And why 30 bits and not 31 bits, or 63 bits, or 120 bits? We may use other 
bases in the future. That's why I prefer to use a common base like base 256. 
And GMP has functions (mpz_import) to load data in base 256, but it's more 
complicate to load data in base 2^15.