C++ string memory management

This sounds very much like the Raymond Chen vs Rico Mariani's C++ vs C# Chinese/English dictionary performance bake off. It took Raymond several iterations to beat C#.

Perhaps there are ideas there that would help.

http://blogs.msdn.com/ricom/archive/2005/05/10/performance-quiz-6-chinese-english-dictionary-reader.aspx

You are stepping into the shoes of Raymond Chen. He did the exact same thing, writing a Chinese dictionary in unmanaged C++. Rico Mariani did too, writing it in C#. Mr. Mariani made one version. Mr. Chen wrote 6 versions, trying to match the perf of Mariani's version. He pretty much rewrote significant chunks of the C/C++ runtime library to get there.

Managed code got a lot more respect after that. The GC allocator is impossible to beat. Check this blog post for the links. This blog post might interest you too, instructive to see how the STL value semantics are part of the problem.