How to Toggle String Case in .Net

Interesting finding in regards to the Case Toggle Algorithm by Robert (see the following code snippet):

protected string ToggleCaseByRobert(string s)
{
    var sb = new StringBuilder(s.Length);
    foreach (char c in s)
        sb.Append(char.IsUpper(c) ? char.ToLower(c) : char.ToUpper(c));
    return sb.ToString();
}

The functionality will stay the same if the line:

var sb = new StringBuilder(s.Length);

is replaced with simplified version:

var sb = new StringBuilder();

but the original version demonstrates about 5...10% performance boost. Kudos to Robert Rohde for this useful tip!