We're in a wholly different world now, C++-compiler-wise.
Current std::stringstream implementations don't have the stated problem anymore, and are just as fast as CDataStream.
The #ifdef'd block does not even compile anymore; CDataStream constructor changed, and missing some std::. Also timing in whole seconds is also way too granular to say anything sensible in such microbenchmarks. Just remove it, it can always be found again in git history.