>As I´m not a VBer, and I´m just starting study C#, I don´t know if that´s the correct way of doing things... anyway, for what people are saying, such code must have similar performance... but, that wasn´t what I saw.

Well, this code isn't completely optimizied. You should be setting the max value of the string builder (you can pass this number to the contructor) so that when the max length is reached, it does not need to reallocate more space for it.