Console.WriteLine slow

If it is just for debugging purposes you should use Debug.WriteLine instead. This will most likely be a bit faster than using Console.WriteLine.

Example

Debug.WriteLine("There was an error processing the data.");

You can use the OutputDebugString API function to send a string to the debugger. It doesn't wait for anything to redraw and this is probably the fastest thing you can get without digging into the low-level stuff too much. The text you give to this function will go into Visual Studio Output window.

[DllImport("kernel32.dll")]
static extern void OutputDebugString(string lpOutputString);

Then you just call OutputDebugString("Hello world!");