No, they get 39 decimal digits (1.7e38 is 39 decimal digits). 127bit chunks would get you 2.36% overhead, which is not bad. However at 93bit chunks can (barely)

No, they get 39 decimal digits (1.7e38 is 39 decimal digits). 127bit chunks would get you 2.36% overhead, which is not bad. However at 93bit chunks can (barely) be encoded in 28 digits (2^93 ~= 9.9e27) and it's more efficient at around 0.36% overhead. So once you have 128 bit arithmetic, it's still not worth using all or most of those bits per chunk, 93bit chunks is the most efficient under 128 bits.