>VFP string manipulation is as fast as the underlying C++ code that implements it.

Agree.

>The only time is slows down at all and where you'd want to resort to using file I/O is when strings are nearing the physical memory size. Once strings get that big you end up swapping virtual memory and preformance drops into the mud.
>If you are working with strings that are up through a couple of megabytes in size you are better off just using string operations.

I think that Cetin is right. The memory reallocation while string concatenation is a common problem for all strings realizations (VFP, MFC, VB etc.) In case of creating large string by appending a small substrings, sequential output to file will be significantly faster. Don't remember exactly, but speed difference of creating a 3 Mb XML (with a 128 MB RAM) may be about 10 times or even more.