I was just about to post this. If I use ostringstream, and also I change the code so it has to construct the StringBuilder every test (at the moment they build

I was just about to post this. If I use ostringstream, and also I change the code so it has to construct the StringBuilder every test (at the moment they build it once and then keep calling 'toString'), then I get the output (from the test program on that website): Accurate performance test: ostringstream took 0.0120331 seconds, and ToString() took 0.0221947 seconds. The relative speed improvement was -45.784% Join took 0.0176613 seconds.